Once a document has been linked in a workpaper you can open the document to view it. You can either view a document in read-only mode, or you can edit the document by checking out the file.
When editing a PDF document, ensure you have PDF editing software installed on your machine, and that it is set as the default program for editing PDF files.
If a document link is broken (that is, the document has been renamed or moved to a different location), then you will not be able to open the document. You must re-link the document.