There are proprietary file formats. For example, MS Word, MS Excel, MS Access, et al...
Paint Shop Pro formats, Adobe PhotoShop, Corel Draw, Sony , a gazillion audio formats, Ad infinitum...
Formats may be patented and only used under the rules imposed by those patents.
PDF, on the other hand, is not proprietary; albeit begun by Adobe (I think)
PDF: Portable Document Format
The whole point of its creation was to have a file format that was portable; meaning, that it would be accessible across many different systems.
Examples: Windows, MAC, & Linux, to mention three major OS's.
The bottom line is that PDF Readers, Writers, Creators, etc, may be Free- or not.
There is a lot of software out there that will read and/or create PDF files for you. Some are free. Others are not.
The choice is yours as to which one you choose to use. They all have their individual, unique pluses and minuses.