I am currently using reader DC Version: 21.1.20145.425325 but have had this happen with previous versions also. I usually have 2 Reader DC windows open with multiple tabs open on each window. I am marking up pdf's on both windows at the same time using either "Fill & Sign" or "Comment" tools. After so long of adding text, check marks or highlighting the menu buttons alsong with pdf tab names will start disapearing and then Reader locks up and if you haven't saved you will lose the work you have done. When you re-open Reader DC it asks you if you want to reload what the info that closed unexpectantly but it will never work and says there is nothing to reload. Because of this I am constantly saving my work but this continues to happen on a daily basis. My IT department cannot figure out why it is doing this. They have deleted and re-inistalled Reader DC so many times it just keeps happening. Any help would be greatly asppreciated.
Comment review and collaborate PDF, Crash or freeze
You may also try to turn off the protected mode for testing (Win Only) Go to Edit > Preferences > Enhanced security > Uncheck 'Enable protected mode at startup' Turn off the Protected mode and Uncheck Enhanced Security > Click OK and reboot the computer once. Note: Please turn on the security after testing to avoid any security risks.
If you are on a company machine or network please try to switch to a personal machine/network and try using the application and check for the issue.
You may also check out the help pages listed beloa and see if that works: