When opening Document Manager through HandiLedger\WorkPapers, the columns in Document Manager may be minimised. As such, you're unable to see the documents.
To resolve this issue, follow the steps below:
Hover your mouse over the top left header bar to click and drag the columns to the right.
Expand each column until you can see all of them.
Once each column is visible, go to Options, General.
Under Columns to Show, click Default, OK.
Restart HandiLedger, and the issue should be resolved.