An invoice parser is a component rather than a process: it takes a document and returns structured fields. That is useful and it is not, by itself, a payables improvement. What determines whether it is worth having is what receives the output, what validates it, and what happens to a field the parser was unsure about. Buying the component without designing those three is where parser projects stall.
What a parser typically returns
Supplier details, invoice number and date, currency, totals, tax breakdown, and lines where it can find them. Better parsers return a confidence value per field and the position on the page, which lets a review screen show the extracted value beside the part of the document it came from. That positional information is what makes review fast rather than tedious.
Validation before anything is trusted
Do the lines sum to the total. Is the supplier one you have. Has this invoice number been seen before for this supplier. Is the date plausible. These checks are cheap, catch a good share of parsing errors, and are usually the caller's responsibility rather than the parser's. Skipping them means parser errors reach the ledger.
The human path for the rest
Whatever is left after validation needs a person and a screen that makes correction quick. Design that path first: it is the part your team lives in. A parser with an excellent accuracy figure and no correction workflow shifts the work rather than reducing it, and shifts it to a place with less structure.
Questions people ask about invoice parser
Should we build or buy a parser?
Buying is almost always cheaper unless invoice parsing is your product. The work you cannot avoid is the validation and the review path, which are yours either way.
Do parsers handle multiple languages?
Many do. Test with the documents you actually receive, since performance varies by language and by layout convention.
What about handwritten annotations?
Usually ignored or misread. Annotations belong as structured notes rather than as marks on the document, for exactly this reason.