The PostScript (.PS) format is a concatenative programming language created originally by Adobe as a simpler version of InterPress, the main advantage of the language is that it is exclusively formed by ASCII characters, so it can be sent by mail without suffering any modification.
Thus, together with the PDF format, it's used to spread files that aren't going to be modified and are ready to be printed over the Internet. But unless you are a printer, it is impossible for you to work out what it says in the document, unless you have a viewer like Ghostscript.
A PDF and PostScript interpreter
Ghostscript is the best-known viewer to decipher and view PS format files. It can also be used to view PDF format files. Furthermore, it allows us to print our documents directly from the application, and even transcode our files from .PS to .PDS or vice-versa, although with certain limitations.
Once we have transformed our work to Postscript, it will be possible to print it without suffering any alterations, without worrying about what program generated the original file: Microsoft Office Word, QuarkXPress, PageMaker, Adobe InDesign, etc. If at a later date you want to view it or print it, just remember, all you need to do is install Ghostscript.