Prince Output

Prince produces PDF files that are compatible with Adobe Acrobat and other PDF viewers. The output can be controlled in several different ways, addressing different aspects of the resulting files.

For the error and warning output log, please see Output log.

PDF Versions and Profiles

The PDF files produced by Prince conform to several different PDF versions, up to PDF 1.7, depending on the chosen PDF Profile and the enabled PDF features.

Prince supports tagged PDF files and optional PDF profiles, which can be selected using the --pdf-profile option on the command-line interface, or the setProfile method if using a server wrapper, or the PDF.profile function in JavaScript.

The available profiles, and the PDF version they are based on, are:

PDF ProfilePDF version
PDF/A-1aPDF 1.4
PDF/A-1bPDF 1.4
PDF/A-3aPDF 1.7
PDF/A-3bPDF 1.7
PDF/UA-1PDF 1.7
PDF/X-1a:2001PDF 1.3
PDF/X-1a:2003PDF 1.4
PDF/X-3:2002PDF 1.3
PDF/X-3:2003PDF 1.4
PDF/X-4PDF 1.6

Prince supports files with the combined PDF/A-1a+PDF/UA-1 and PDF/A-3a+PDF/UA-1 profiles.

Prince also uses:

PDF 1.5

  • if object streams are enabled, or
  • if tagged PDF is enabled, or
  • if 16-bit images are included in the PDF;

PDF 1.6

PDF 1.7

To enable tagged PDF without using one of the profiles that already imply it, the command-line option --tagged-pdf can be used.

Prince supports PDF object streams to reduce the size of tagged PDFs. This can be disabled by the command-line argument --no-object-streams or from JavaScript via the PDF.objectStreams boolean property.

Object streams are enabled by default, therefore Prince produces files with PDF version 1.5 - unless a profile that requires older PDF versions will automatically disable object streams.

Choosing one profile over another can help producing a PDF file which has the right properties for its intended destination. Each PDF profile places restrictions on the features allowed in a PDF file in order to achieve its aims. Please also see the Color Management section for the impact the PDF profiles have on color management. Prince produces error messages when the restrictions are not respected.

    $ prince foo.md --encrypt --no-embed-fonts --pdf-profile="PDF/A-1b"
    prince: error: PDF/A-1b does not support encryption
    prince: error: PDF/A-1b requires fonts to be embedded

Generally speaking, PDF/A profiles were created with the goal of long-term preservation of the documents (PDF for Archiving), while PDF/X profiles were created to address publisher's needs in the graphic arts industry (PDF for eXchange). The PDF/UA profile is a standard for producing accessible electronic documents (PDF for Universal Accessibility).

PDF/A

  • PDF/A tries to maximize device independence
  • Audio and video content is forbidden
  • All fonts are embedded
  • Colorspaces should be specified in a device-independent manner: all color data must be Grayscale, CMYK or named Spot Colors and there must be an output intent. Transparency is not allowed. See also Color Management and PDF Profiles
  • Encryption is forbidden

PDF/UA

  • Content must be tagged in a logical order
  • Tags must correctly represent the semantic structure (headings, lists, etc.)
  • Content not accessible to assistive technology must be avoided
  • Meaningful images and graphics must contain alternative text descriptions
  • Security settings must allow assistive technologies to access the content
  • All fonts must be embedded
  • Text must be mapped to Unicode

PDF/X

  • PDF/X is intended to support "blind exchange", i.e. no exchange of technical information is needed to render the printed page as intended
  • Audio and video content is forbidden
  • All fonts are embedded
  • Colorspaces must be specified in a device-independent manner - an output intent is required (see the --pdf-output-intent command-line option in the PDF Output Options section)
  • See the Color Management and PDF Profiles section for the color profiles available in each PDF/X version. Transparency is not allowed, with the exception of PDF/X-4
  • Encryption is forbidden

PDF Accessibility

Producing accessible documents is very important when documents are to be shared with a wider audience. There are several criteria that need to be addressed, summed up in the Web Content Accessibility Guidelines, often abbreviated to WCAG, a set of guidelines for improving web accessibility.

The relevant criteria for producing accessible PDF can also be found in a separate document, the PDF Techniques for WCAG 2.0.

A first step would be to produce files with one of the PDF profiles addressing accessibility, namely the PDF/UA-1 profile or the combined PDF/A-1a+PDF/UA-1 or PDF/A-3a+PDF/UA-1 profiles, by specifying the --pdf-profile command line option. See PDF Versions and Profiles for details.

The next step would be to specifically check compliance of the document's content with the requirements. A number of resoures or tools can be helpful in this step:

Prince helps in creating accessible documents. Note, however, that Prince does not create WCAG-compliant documents by itself - care has to be taken, and the HTML source has to be coded in specific ways to address all requirements in order to create WCAG-compliant PDF documents.

Bruce Lawson has written an interesting introduction on how to make accessible tagged PDFs with Prince - all you need to know about PDF tags and Prince! Last but not least, there is a nice Resources page on tagged and accessible PDFs.

PDF Features

Prince supports a wide range of PDF features, including the following:

PDF Links

Prince supports PDF-internal and -external links. HTML hyperlinks are automatically converted. To make an element in XML, or any arbitrary element, a clickable link, the prince-link CSS property is required.

    xref {
        prince-link: attr( linkend )
    }

The property prince-pdf-link-type may be used to control the link type and target, i.e. whether relative links should be embedded in the PDF as web (URL) links or file links (by default they will be resolved against the base URL of the input document) and whether to open the links in the same or a new window. Note however that the optional link target keywords same-window and new-window only affect links to local PDF files.

    a[href] {
        prince-pdf-link-type: new-window;
    }

This example is equivalent to prince-pdf-link-type: auto new-window and has only effect for links to local files.

Prince also supports the following PDF-specific fragment identifiers, supported by web browsers, and will use them when generating links to local PDF files.

    <a href="test.pdf#page=2">...</a>

    <a href="test.pdf#nameddest=section1">...</a>

Named destinations (nameddest) in PDF files have a similar function to HTML IDs: they can be the target anchors for links from other documents. The property prince-pdf-destination is used for creating them.

HTML

    <div class="section" data-sectionid="section1">

CSS

    div.section {
        prince-pdf-destination: attr( data-sectionid )
    }

In order to link to this section, the following syntax is used:

HTML

    <a href="test.pdf#nameddest=section1">...</a>

PDF Actions

Prince supports the pdf-action: URL scheme for PDF actions. Typical values are Print, GoBack, GoForward, NextPage, PrevPage, FirstPage, LastPage.

    <a href="pdf-action:Print">Print Document</a>

However, Prince passes the provided values verbatim to the PDF viewer, so the user can supply values that Prince doesn't know about, but the viewer does. Also, these scripts will always be run, unlike JavaScript (see Applying JavaScript in Prince).

Please be advised that this and the following actions and scripts are dependent on the PDF viewer, and in many cases might only work in Adobe Acrobat products.

The property prince-pdf-open-action may be used to specify a space-separated list of actions to perform when the PDF file is opened, like eg. popping up the print dialog box automatically, or setting the default zoom level for PDF documents. Any arbitrary identifier can be specified, although these may be PDF viewer specific; Acrobat can take just about any menu item.

    @prince-pdf {
        prince-pdf-open-action: zoom(fit-page) print;
    }

In a similar fashion, scripts that will be executed when the PDF file is opened may be included with the prince-pdf-script property. A common use case is to activate the "Print" dialog automatically. To achieve the equivalent of the previous example, the following code could be used:

    @prince-pdf {
        prince-pdf-script: "this.zoomType = zoomtype.fitP; this.print();"
    }

The property can also take the url() function to reference an external JavaScript file.

    @prince-pdf {
        prince-pdf-script: url("myscript.js")
    }

Prince offers yet another way to include scripts in a document through a stylesheet: the prince-pdf-event-scripts property can be used to include JavaScript code that will be executed in the PDF when printing, saving, and closing the PDF, known as "Document Action" scripts. Just as with the previous property, scripts can either be given inline, or be included from an external file.

    @prince-pdf {
        prince-pdf-event-scripts: will-close url("onclose.js"), will-print url("onprint.js");
    }

PDF Pages

Prince allows for some degree of control on the pages and the page layout in a PDF file. The CSS property prince-pdf-page-label can be used to set the page label that will be displayed in the PDF viewer. It can be used to instruct the PDF viewer to display the page label in the ToC in a particular way.

    @page {
        prince-pdf-page-label: counter(page, lower-roman);
    }

The property prince-pdf-page-mode can be used to set the default page mode for the PDF file when it is opened. For example, whether the bookmarks panel should be displayed, and whether the viewer should be fullscreen.

    @prince-pdf {
        prince-pdf-page-mode: fullscreen;
    }

Also the default page layout for the PDF file when it is opened can be determined with the prince-pdf-page-layout property.

    @prince-pdf {
        prince-pdf-page-layout: two-column-right;
    }

The values of this property are mapped to PDF page layout options:

CSS Keyword PDF Page Layout Description
single-page Single Page View Displays one page at the time
one-column Enable Scrolling Displays pages in one continuous vertical column
two-column | two-column-left Two Page Scrolling Displays facing pages side by side in a continuous vertical column - the first (i.e. cover) page is on the left.
two-column-right Two Page Scrolling & Show Cover Page Displays facing pages side by side in a continuous vertical column - the first (i.e. cover) page is displayed alone on the right.
two-page | two-page-left Two Page View Displays a two-page spread at the time - the first (i.e. the cover) page is on the left.
two-page-right Two Page View & Show Cover Page Displays a two-page spread at the time - the first (i.e. the cover) page is displayed alone on the right.

PDF Printing

Prince also provides two properties to fine-tune the printing of the PDF. The property prince-pdf-print-scaling can be used to disable print scaling for the PDF file when it is printed and the property prince-pdf-paper-tray controls the PickTrayByPDFSize flag in generated PDF files, which specifies whether the PDF page size is used to select the input paper tray.

Duplex printing is supported with the CSS property prince-pdf-duplex. This property may be used inside the @prince-pdf at-rule to set the Duplex property in the PDFViewerPreferences dictionary. The values duplex-flip-short-edge and duplex-flip-long-edge tell about how to flip the paper, while the value simplex suppresses duplex printing.

    @prince-pdf {
        prince-pdf-duplex: duplex-flip-long-edge;
    }

PDF Compression

Prince compresses its PDF output to reduce the size of the documents that it produces, but does not create linearized PDF files, as this would increase formatting time and memory requirements. An external program such as Adobe Acrobat or Ghostscript may be used for this purpose if necessary.

Compression may be disabled with the command-line option --no-compress.

PDF Encryption and Document Security

Prince can encrypt the produced PDF files with the --encrypt command-line option. The default key size is 128 bits. With the option --key-bits a different key size can be chosen. Also the JavaScript methods PDF.encrypt and PDF.keyBits can be used for the same purpose.

The command-line options --user-password and --owner-password set respectively the PDF user password and the PDF owner password.

Prince also offers a range of command-line options to disallow printing, copying, annotating and modifying the PDF output: --disallow-print, --disallow-copy, --disallow-annotate and --disallow-modify.

PDF Font Embedding and Subsetting

Prince embeds fonts in its PDF output to ensure accurate viewing and printing on any system. Typically, only the necessary parts of a font will be embedded - font subsetting is enabled by default.

Font subsetting can be disabled with the command-line option --no-subset-fonts or with the JavaScript function PDF.subsetFonts: in that case, Prince will embed the entire font in the PDF file, which is convenient if people are planning on editing the PDF file later, and may need to add glyphs that were not present in the original PDF.

Font subsetting is disabled automatically for individual fonts that do not grant permission to subset, or if Prince cannot subset them for some other reason.

Font embedding can be disabled if necessary, for example if Prince is being used to create PDF files in a controlled environment with known fonts where space is at a premium. The command-line option --no-embed-fonts is used for this purpose.

PDF Attachments

Prince supports adding files to PDF documents as attachments. The main mechanisms for doing so are the JavaScript function PDF.attachFile and the command-line option --attach. Additionally, the job description JSON format, used by the Prince Control Protocol, can be used to provid an attachment "inline" through the Java/C# APIs (see Prince Wrappers) instead of as a separate file on the filesystem. See Prince Control Protocol for details on the job description JSON format.

PDF Bookmarks

Prince can create PDF bookmarks that link to document content.

Bookmark levels

PDF bookmarks have numeric levels that place them in a bookmark hierarchy. For example, a bookmark at level 2 can contain nested bookmarks at level 3, or any higher level. The level of a bookmark is controlled using the prince-bookmark-level property, shown here being applied to the XHTML heading elements:

    h1 { prince-bookmark-level: 1 }
    h2 { prince-bookmark-level: 2 }
    h3 { prince-bookmark-level: 3 }
    h4 { prince-bookmark-level: 4 }
    h5 { prince-bookmark-level: 5 }
    h6 { prince-bookmark-level: 6 }

The default value for this property is none, which inhibits the creation of a bookmark for the element.

It is possible to control the state of the bookmark, i.e. whether the bookmark is in an open or closed state, with the prince-bookmark-state property. In this way you can close each chapter and hide the subsections for documents that are very long, or you can choose to have a deep bookmark tree.

Bookmark labels

PDF bookmarks have textual labels that by default are copied from the text content of the element that generated the bookmark. The text of this label may be controlled using the prince-bookmark-label property, shown here being applied to a chapter element that has a title attribute:

CSS

    chapter {
        prince-bookmark-level: 1;
        prince-bookmark-label: attr(title)
    }

This property can take any content value, including literal text strings and counters. See Generated Content Functions.

Bookmark targets

PDF bookmarks are links that display a particular part of the document when activated. By default, a bookmark will link to the element that generated the bookmark, which is sensible behavior for bookmarks generated from headings or chapter elements. It is also possible to change the target of a bookmark using the prince-bookmark-target property, which takes a URL directly or an attribute containing a URL:

CSS

    bookmark { prince-bookmark-target: url(#intro) }
    bookmark { prince-bookmark-target: attr(href) }

The default value for this property is self, referring to the element that generated the bookmark.

PDF Tags

Tagged PDF files have special handling mechanisms for specific tag types. When enabling tagged PDF files with the command line option --tagged-pdf Prince automatically assigns default values to certain HTML elements, which can be seen in the default html.css style sheet (see Installation Layout).

However, in specific cases it is advisable to fine-tune the PDF tags with the prince-pdf-tag-type property. In Prince, it is possible to assign PDF tag types to elements in the document through the prince-pdf-tag-type property, in order to create XML vocabularies in the PDF.

CSS

    ul.toc {
      prince-pdf-tag-type: TOC;
    }
    .toc li {
      prince-pdf-tag-type: TOCI;
    }

HTML

    <ul class="toc">
      <li>First Chapter</li>
      <li>Second Chapter</li>
    </ul>

The possible values are the following PDF tag types:

  • Part
  • Art
  • Sect
  • Div
  • Index
  • BlockQuote
  • Caption
  • TOC
  • TOCI
  • P
  • H1
  • H2
  • H3
  • H4
  • H5
  • H6
  • OL
  • UL
  • LI
  • Lbl
  • DL
  • DL-Div
  • DT
  • DD
  • Span
  • Quote
  • Table
  • BibEntry
  • Code
  • Figure
  • Formula
  • Artifact

The default value auto leaves the tag assignment to Prince.

Bruce Lawson has written an interesting introduction on how to make accessible tagged PDFs with Prince - all you need to know about PDF tags and Prince!

PDF Metadata

Prince creates PDF metadata from the content of the XHTML metadata elements. The content of the <title> element is used for the document title, while the <meta> element can be used to specify the document author, subject, keywords, date, and generator application:

XML

    <html>
    <head>
    <title>Cooking with Cabbage</title>
    <meta name="author" content="John Smith"/>
    <meta name="subject" content="An interesting book about food"/>
    <meta name="keywords" content="cabbage, cooking, eating"/>
    <meta name="date" content="2009-04-01"/>
    <meta name="generator" content="MyReportingApp"/>
    </head>

XMP Metadata

Additionally, XMP metadata can be added to a PDF file from an XMP file. This file needs to be passed to Prince either via the --pdf-xmp command-line option, the prince-pdf-xmp CSS property, or it can be specified in JavaScript with the PDF.xmp() function.

The PDF.xmp() JavaScript function, the prince-pdf-xmp CSS property and the --pdf-xmp command-line option require either a URL pointing to an XMP file, or an encoded data: URL.

Prince includes data from the <x:xmpmeta> element and its contents. The xpacket processing instructions are ignored, as Prince generates those itself when it produces the PDF file.

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