Acrobat Reader Xi

If you opened a malicious PDF that tried to install a virus, Reader XI would essentially trap the virus inside a digital jail cell. When you closed the PDF, the cell vanished. It was Adobe’s admission that PDFs were dangerous, but their solution was so elegant that modern browsers (like Chrome's own sandbox) still use the same architecture today.

If you need to view PDFs, you should uninstall Adobe Reader XI and install the modern equivalent: acrobat reader xi

More controversially, Reader XI allowed limited text editing if the document creator enabled the rights. This created a weird office dynamic where managers would send a "Reader Extended PDF," and the employee would spend 20 minutes trying to move a single line of text down one pixel, only to accidentally delete a signature block. If you opened a malicious PDF that tried