This is a good choice for file conversion for free online. It allows you to convert to and from many formats, including MS Word DOC to PDF, not to mention PostScript to PDF, but there are a number of other possibilities as well. Unfortunately, the input file may be not larger than 1 megabyte, which rules out long treatises.
These two sites allow you to create PDF files from PostScript files for free online, using ghostscript. Babinszki world is probably preferable, because it's free of advertisements. However, for a long-term solution, I would recommend simply installing ghostscript on your own machine.
This site is handy if you want to get a better impression of what a particular PDF file, PostScript file, or Word file contains and you don't have the necessary viewer installed. (For me, this happens often with MS Word files!) It does an okay job but remember that it's for viewing and not for printing. If you need to print an MS Word DOC file, you might try to convert it to a PDF file first, using Document Converter eXPress, mentioned above.
http://pinon.sdf-eu.org/covers/file_conversion.html