If you create bookmarks to some PDFs and afterwards delete the PDF or move it to another place, there's no way to know if a bookmark is still valid. First if you try to open it, Okular will tell you in a dialog that it's not available. Therefore it would be convenient if Okular checked those bookmarks e.g. on start, when the bookmark tab is opened, when the user tries to open an invalid bookmark, etc. and if not available marks those in some way, e.g. with a gray font or striked out.
Would be nice. See also Bug 380330.
Sorry but that is not a good idea, if you have 10000 files, do we have to stat the 10000 files when you start Okular? What if those 10000 files are on the internet, do you want to do 10000 connections to see if the files are still there? More over, why only check on application start? The files the bookmarks point can be removed at any point of time, can't they? So we would need to install 10000 file monitors just in case you remove the files. This is just not possible.
Wow, I doubt someone is using Okular's bookmarks to this extent or do you? :) Having around 30 booksmarks I already found cumbersome to manage, but 10,000 sources? Are we talking about the same topic? I was talking about reference to pages in PDFs (rightclick, bookmark). I would also not know how you'd bookmark websites at all.
Sorry, please forget about out the comment about websites -- I misread it.
Maybe this could then be triggered manually and the user could mark a bookmark as non-local to exclude it or to mark it in a different way? I mean, somehow you need to manage your 10,000 bookmarks. ;)