A supplier sends the same invoice twice - a reminder with a new file name, or the bookkeeper filing it again. Left alone, that is how one invoice gets paid twice. BillSight is looking for exactly that.
Two files in the month's folder: google-2026-09.pdf and google-invoice-copy.pdf. Different names, and nothing about the file names says they are the same invoice. The numbers on them do.
Add the folder, or the two files, as you would any other invoices.
It says duplicate (1) and names the file. Clicking it takes you to the row.
Delete the second row, or keep both if they really are two invoices - the point is that you decided, rather than finding out later.
Not on the file name, not on the file size, not on the date. Two files with the same supplier and the same invoice number are the same invoice, whatever they are called.
It compares every invoice in the run against every other one, so the pair does not have to sit next to each other in the folder.
The export history records which invoices went into which file, and can be searched by invoice number - so "have I sent this one to accounts?" has an answer too.
Turning a month of invoices into one spreadsheet · Proving what arrived, and that it has not changed · Keeping the invoices off somebody else's server
Everything happens on this computer - your invoices are never uploaded.