While trying to find a specific project I recalled, I encountered this list of projects which might be of interest: https://github.com/tstanislawek/awesome-document-understandi...

The project I had in mind was similar to this one but I can't remember the name currently: https://github.com/tabulapdf/tabula

However, if you're looking for a ML-based, invoice-specific project looks like the other comment to your reply might be more useful.