The main software for viewing PDFs is Adobe Acrobat Reader or Adobe Reader. The software evolved over time in its evolution, making space for the work of other companies that were able to provide smaller and lighter software to open PDFs.
But anyway, the best software and the ultimate solution to open PDFs in the event of problems with other software is still Adobe Acrobat Reader, and can not be ignored anyway. Hence, Downloader puts it as its main software.
However, as the main developer of Adobe’s PDF technology, the first versions that can support all of the new features of PDFs are Adobe Readers.