I tried LibreOffice Draw. With Draw it’s possible to delete pages and export as Pdf and set passwords.
Btw Draw isn’t displayed in the apps menu (9 dots).
LibreOffice Writer=>click lower x to close the unsaved document=>Draw Drawing=>File=>Export as=>Export as PDF=>tab Security=>Set passwords=>enter your passwords=>click OK=>click Export
I didn’t try to add pages but I suppose that it works, too.