The first is called Layout Based.

It is linked to the layouts and obliges the user to intervene at the start to build the invoice mask for each supplier. The Layout Based method obliges one to go through this long and tiresome learning phase.

The second, more recent, is called FreeForm Based.

It plunges into the document and uses techniques of artificial intelligence to extract the relevant accounting elements from the invoice according to the relations of the various elements.
For example: the total invoice will be found on the right or below the indication "To be paid".

Although allowing an IMMEDIATE recognition of the invoices, this method may encounter difficulties with the so called “exotic” invoices e.g. those whereby the format is not standard or where the indications are laid out vertically, etc.
The FreeFrom Based method has a recognition rate that reaches a certain limit.