Coolmuster PDF Encrypter works, but enlarged a test PDF -- I saved today's GOTD page to PDF in Firefox -- from around 1/2MB to just under or just over 2MB in size, depending on if I allowed printing hi or low rez. You have the option to set a password to open the file &/or alter it, 3 types of encryption, and 7 different permissions you can make available, e.g., printing. Coolmuster does not say anything about the compatibility of the encrypted PDFs that I could find, so you'd have to test to see how well [or if] the enrypted PDFs worked on any non-Windows devices, and possibly the different apps that might be used to open the PDFs.
I monitored the install in a Win11 64-bit VM -- it is Win11 compatible. You get the program's folder in Program Files (x86), 2 folders in Documents, & 1 Coolmuster folder in Users\ [UserName]\ AppData\ Roaming\. The registry gets a single new key for uninstall.