Sometimes the communication between the PDF Compressor service and the worker process PDF_CompServer.exe breaks and the application crash.
The error looks like this:
Wed Mar 22 14:56:26 2023: Error: Cannot access background worker #1
The reason could be many and that's why we need some help from users like input files causing the shut-down of the process, dump and log to go deeper and localize the origin of the crash.
Please create the following registry key, so crash dump can be written:
- Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Windows Error Reporting\LocalDumps\pdf_compserver.exe
- Open the Windows Registry
Look for the path \HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Windows Error Reporting\LocalDumps\
Once there, make right click on LocalDumps → New → Key → Name it pdf_compserver.exe
You should find all the dump files related to the crash on the following path according to the service user %LOCALAPPDATA%\CrashDumps or C:\Users\<serviceuser>\AppData\Local\CrashDumps
Another way to create dump file is by opening Task Manager → right-click on PDF Compressor Service → create a dump file
Please check as well if there are any messages in the event log (eventvwr ) related to PDF_CompServer.exe? Click on Start, type eventvwr (Windows Protocols →Application Error). 
Open the PDF Compressor and set logging to "specific information for debugging" in File→Options→Configuration→Logfile, process the files again 
After you have collected all the files, send them to pdf_compressor@foxitsoftware.com
