Before Microsoft popularized the "Ribbon" interface, Adobe used classic toolbars with clear text labels. Modern versions hide essential tools behind hamburger menus and floating panels. Millions of users prefer the logical, menu-driven layout of older versions. Everything—print, zoom, rotate, view—is one click away.
The latest versions can be resource-heavy, sometimes causing lag or taking up to 40 seconds just to open a file. Older versions are generally more "lightweight" and faster on aging hardware.
While the benefits of a stripped-down, fast PDF reader are clear, downloading an old version of Adobe Acrobat Reader is not a decision to be taken lightly.
The most significant argument for legacy versions is performance. Older versions of Adobe Reader (such as version 9 or XI) were engineered for hardware from the late 2000s and early 2010s. Consequently, they are incredibly lightweight by modern standards.