Most actual poisoning techniques don't actually work that well. When I end up with a PDF, I usually strip out the existing text layer, apply a denoiser and a few other preprocessing steps to correct common errors, then a layout / reading order detector, and finally OCR the different blocs. This is against the most common poisoning techniques, and one of the most efficient, called : someone printed a document, forgot about it for 3 years, then scanned it slightly tilted (and dirty, crumpled, ...), and the scanner decided to apply its crappy OCR.

Using screenshots of the PDF also avoid any kind of font face poisoning, and anti copy protection.

If you really, really need to protect your PDF, please consider accessibility first, then what would work imho is to use the scripting features of pdf to actually render your content on the fly. That would probably mess up most of the "automatic" processes.