Problem: Citoid doesn't solve the url when the link is a PDF document, giving an error message.
Proposed solution: Enable citoid to get the metadata from the PDF and fill the fields required.
Who would benefit: All editors, especially the users of the VisualEditor.
More comments: As user Mvolz commented, maybe it is tricky to automatically assign which kind of cite corresponds to the file (journal, book, etc). If the metadata doesn't provide this information, a solution could be to let the user select the appropriate one.