I have a resume in PDF format. I have seen people linking to PostScript versions of their resume.
I am not sure why they do that yet. How can I convert my PDF document to a LaTeX/PostScript document?
You can convert PDF to PS (PostScript) pretty easily, because they are related as both were designed by Adobe. PDF is more or less the modern re-spin of PS. However, the resulting quality might vary depending on the document and the converter. Also there should be no reason to provide PS versions of a resume nowadays. For normal users PS is outdated. It might still be useful for print back-ends in some cases.
On the other hand, it is not really possible to convert a PDF to LaTeX. There is a question about this already: How to convert PDF to (La)TeX?. Basically you can't recover all formatting from the PDF (or MS Word) and produce a good LaTeX code file from it.
If you already have a good looking PDF just stick with it. Alternatively you can extract the text from it (e.g.