— Adobe Reader has always been a free PDF viewer, while "Adobe Acrobat Professional" is a paid product. Version 8.1.0 is very old (released around 2007) and is no longer supported by Adobe.
Released initially in November 2006, with the 8.1.0 update arriving in June 2007, Adobe Acrobat 8 Professional was part of the Adobe Creative Suite 2.3. For its time, it was a groundbreaking piece of software. It made the creation and editing of PDFs accessible to professionals without requiring the steep learning curve of modern tools. For many, this version represents a "golden age" when you could buy the software outright with a one-time fee, rather than paying a monthly subscription. — Adobe Reader has always been a free
You do not need to risk infecting your computer to view or edit PDF documents. Highly capable, secure, and completely free alternatives exist today. Adobe Acrobat Reader (Modern Version) For its time, it was a groundbreaking piece of software