A business that invests in building a machine that reads data, produced by a 3rd party machine, using format intended for lay humans to read, is not investing in the right tech IMO.

Small-mediums should be looking to consolidate buying through a few good suppliers and working with them directly to automate process, or adopting interchange formats.

Problem for some small-business is the cost (process changes, licencing etc) of adopting interchange formats and working with large vendors is prohibitive at their scale e.g. the airline BSP system.

I agree that solving the problem generally i.e. replacing an accounts payable staff person capable of processing arbitrary invoice documents will be comparable to self-driving in difficulty.

If a company deals with a lot of a single type of PDF, then the approach could be economical. I am actually involved in a project looking at doing this with AWS Textract.