I have a left and right justified text, with no indentation at the start of a paragraph. To signal the end of a paragraph, it is useful that the last line of each paragraph has some white space at its right site. I try to do this by adding some no-break spaces as follows:

p:after {content: '\A0\A0'}

Yet, in the pdf there is sometimes a line-break just before these no-break-spaces. How can I avoid this?

You could use JavaScript to add the spaces directly to the text following the last word.