Documents
Every file attached anywhere in ZenBooks - receipts, scanned invoices, generated PDFs - shows up here, whether or not it's linked to a voucher yet.
Unattached vs. all
The Unattached tab is the useful everyday view: files uploaded but not yet linked to a voucher - a running "still needs bookkeeping" list. The All documents tab is the complete archive, attached or not.
Attaching a document
A document can be linked to an existing voucher, or used as the starting point for a brand-new one - the same quick-capture idea the Journal page's draft vouchers support, just starting from the file instead of the ledger entry.