A small suggestion, this may not fix your issue, but it's worth checking:
When you open Adobe, go to the Edit Menu > Preferences > Security (Enhanced) and check if the 'Enable Protected Mode at Startup' option is enabled. I remember working with Adobe Reader a while ago on a project in which I had to read a PDF file and when I turned this setting off in Adobe Reader it allowed me to work with the file after that. I believe it's a security protection mode that is available. You can turn it off for that file only to see if it makes a difference.
Hope this helps!
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Jorge Barajas
Blue Prism
Senior Product Consultant
Austin, Texas
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Jorge Barajas
Blue Prism
Senior Product Consultant
Austin, Texas