I have a table with two columns. If i have defined a width of the left columns to be 100px, and have text in the right columns, e.g.

<table cellpadding="0" cellspacing="0" border="0" width="100%">
                        <tr>
                            <td width="100px"></td>
                            <td width="260px">Some text</td>
                        </tr>
                    </table>

When I convert to PDF, it is not keeping the width of the first cell. Can this be done?

In general the HTML presentational attributes don't require "px", they just take a number that gets treated as a pixel measurement. Only the CSS properties use explicit units. So width="50" or style="width: 50px" are usually equivalent.