Našel jsem nějaké skripty, ale pro starší verzi Acrobat Readeru, s novějšími nemusí fungovat - musely by se upravit.
https://www.autoitscript.com/forum/topic/25659-silent-pasword/
https://www.autoitscript.com/forum/topic/178774-pdf-password-protect/
https://www.autoitscript.com/forum/topic/191197-open-pdf-in-auto-it/
https://www.autoitscript.com/forum/topic/41014-how-to-open-pdf-file-that-has-a-password/
atp.