I have iOS devices -- be that good or bad. When I download a manual from Canon's USA support site, it has a lock on it. I think that causes "Books" (the place where iOS stores PDFs) and I guess also Preview (the PDF viewer on iOS and macOS) to not allow adding annotations or bookmarks.
One option is to open the PDF in Preview and then "Print" the entire thing as a PDF but that loses the hyperlinks.
Curiously, I've brought this topic up before in a forum (I don't remember which one, it might have been this one) and one person said that they can add annotations and bookmarks in iOS just fine but I never asked which site the person got their PDF from.
My suggestion is to release the manuals unlocked or publish the password somewhere.
