Re: convert .tex file
.tex files are not so much a format as input for a typesetting program. Your files could be TeX or LaTeX input, you have to find out. These would be processed by the tex and latex commands respectively. Your files may also include some additional style files, so you need those installed. The output from tex or latex is DVI format, which can be converted to Postscript using dvi2ps. From there you can generate PDF using pstopdf (or is it ps2pdf?).
It would be ps2pdf. As an alternative you can use the commands pdftex or pdflatex to convert your *.tex input directly into a *.pdf file. The method suggested by ken_yap has one big advantage though: If your input file includes eps pictures, they will be preserved in the final PDF. If not and you want small file sizes go the direct way.
Technology is 'stuff that doesn't work yet.' -- Bran Ferren