How can I label specific handwritting area in a PDF

Hi !

For a project I want to do a handwritting recognition of code like “AA45DC”
There are in specific area in a PDF (around 50 for one PDF).

I would like to know how can I use label studio to label those code.
For what I see I can’t put directly the PDF, do you have a solution in mind ?

Thanks for your help ^^
Have a good day
Yann SADOWSKI