Error - The document could not be saved. There was a problem reading this document (105).

Hi @Arthurjohnston 

Sorry to hear about the trouble caused

When do you get this error message? Is it when opening the file or when trying to access any feature?

The cause of the error is there's something corrupted in the PDF file's data. It could be anything, and identifying that is quite difficult.

That is why Optimizing pdf and saving it as a PDF printer was suggested because this feature regenerates the file. 

Let us know if you receive this error with multiple PDF files.

Update your Acrobat to the most recent version 

Go to Acrobat> Help > Check for updates and reboot the computer once (you must save all the work before restarting)

To download the patch manually, more information about this release is here: Release Notes | Adobe Acrobat, Reader 

If it continues to through the error, disable this setting once and see if that works. 

Navigate to Acrobat>Menu>Preferences>Security (Enhanced)>disable "Protected Mode at Start-up", "Protected View" and "Enhanced Security">OK>close and reopen Acrobat

Thanks,

Akanchha