When your Bank Mellat statement arrives as a scan or a photo of the page rather than a clean export, the numbers on it are just pixels until they are extracted. A statement document that was printed and then scanned, or photographed with a phone, introduces extra noise. Paper grain, angled capture, uneven lighting, and slight blurring all work against clean data extraction. The engine applies optical character recognition to these images and then runs the same running-balance check it performs on a native digital file. If a 3 is misread as an 8, or a digit pair merges, the total no longer adds up and the row is flagged. That flagged row stays in place; the rest of the file remains intact and ready to review. You can correct the one misread line without redoing the whole conversion.
Whichever order your Bank Mellat statement prints its columns in, each one still has to land in the right place once it reaches a spreadsheet. Column mapping takes the fields the engine identified in the statement and places them into the export layout you choose. Date, description, debit, credit, and balance each go into their own column, in the order your accounting package expects. Map once for a particular layout and the mapping holds for every statement that shares that structure. If a scanned document is missing a column or the engine cannot reliably place it, that column is left blank rather than being guessed. You see what is absent before you export, so nothing lands in your ledger without your approval.