that should still be the file from PDFCreator 1.7.3.
As a first attempt, please uninstall PDFCreator 2.5.2, restart your computer and check if the pdfcmon.dll is still there. If it is gone, you can now install v 2.5.2 again and this time it should work.
If it is still there,
please take the following steps to fix the problem:
1. Run cmd.exe as admin
2. enter the command "net stop spooler" (leave the cmd open afterwards, you will need it again in step 4)
3. Delete the pdfcmon.dll
4. in cmd, enter the command "net start spooler"
5. Run the setup for PDFCreator 2.5.2 again