The adobe reader shows me this error: "There was an error opening this document. This file is already open or in use by another application" when we are opening a pdf generated by another application. We checked that the pdf file was not read-only and no other software was using this pdf. It was strange because some PCs could open the file and some other couldn't, and after some period of time the file could be opened again. This happened usually on those files with more than 20 pages. We have searched on the Adobe website and without any solution can solving this issue. Only suggestion is using other viewer but it is not the user like to have.
General troubleshooting, Standards and accessibility
Hope you are doing well and sorry for the trouble. as you are unable to open the PDF and getting the error 'There was an error opening this document. This file is already open or in use by another application'
Would you mind sharing the workflow/steps you are doing to open the file? If the file is stored on a shared network/drive please download it to your computer first and then try to open it with Acrobat/Reader DC and check.
Also make sure you have the latest version of the application 21.05.20058 installed. Go to Help > Check for updates and reboot the computer once.