The PDF format does actually let documents instruct PDF processors to disallow printing [0]; Acrobat Reader (if nothing else) presumably respects these instructions, even though they're obviously possible to work around.
[0] e.g., https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandard..., p. 123, Table 3.20, "User access permissions", and probably others that I can't find right now
First, you could screenshot each page, and print that. That's a lift.
Second, It's not that hard to extract text from pdf file formats. That's also a lift.
but like, it's not that complicated. yes, text flow, font selection, on and on, but it's just postscript. Pull the text and print it. It's signed not encrypted. It's challenging to implement pdf. javascript support is nuts, for example.
But if you just want to pull the text? there's not much to it.
Pay the author. It's not much. But like, it's not locked down.