If you use texmaker to compile LaTeX files, you must have experienced the issue where PDF files generated with the Quick Build option are marked as modified, and you must save them (or refuse) even if you simply wanted to see a preview of the document.
This is due to the fact that, by default, the Quick Build creates a PostScript file which is then converted to PDF by Preview -- that's why Preview marks it as modified (as new, actually, to be more specific). The solution is change the Quick Build command: Preferences » Quick Build » LaTeX + dvipdfm + View PDF, or the next option, LaTeX + dvips + ps2pdf + View PDF. As I don't use the PostScript file, I only create the PDF file. I've had some problems with the PdfLaTeX, so I'm not mentioning it here.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20081203092237254