Adobe Acrobat Reader DC Install for all versions
https://get.adobe.com/reader/otherversions/
Adobe Acrobat Reader DC software is the free global standard for reliably viewing, printing, and commenting on PDF documents. And now, it's connected to the Adobe Document Cloud...
PDF - Wikipedia
https://en.wikipedia.org/wiki/PDF
Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1993 to present documents, including text formatting and images...