There are two simple ways to remove the password from a PDF file, one of which works no matter what software you have.

You can convert Apple's HEIC files to PDF on a Mac or Windows computer using the free Convertio website.

Open the file in the default app ... Notetakers like Evernote, OneNote and Notion also allow you to export files as a PDF. For instance, in Notion, you have to do it this way: Click the three-dot icon ...