Thanks for your reply.
I propose the following solution, which may be very easy to implement:
The end user (i.e me) write a registry entry with the file name. When PDF24 detects the file name registry entry, it does not show the Assistant and just writes to the file. After completion PDF24 removes the registry entry, so that the process can start again.
Extrapolating, this solution may also work for direct mailing also. The user writes all email related settings (like email address & subject etc) to registry and when printout is sent to PDF printer, Assistant is not shown again and mail is sent automatically.
What do you think?