Mr. Whiskers was quite accomplished in his fields of expertise at the time, namely napping, prowling, and scrapping.

gImageReader or ocrmypdf will get you the pdf text, but after the text will need fiddling with and cleaning. Use LibreOffice, languagetool, write-good, etc to make finding the oddballs easy.

pdftk is what you want for editing pdf metadata.

Gimp is what you’ll need for editing images, Looking for watermarks, smoothing edges, lowering quality, introducing random noise, etc.

exiftool is what you’ll need for image metadata. Or take a screenshot, add a bit of noise or de-noise, and add back to the new pdf.

Scrivener or LibreOffice if you want to polish/republish, though that’s a ton of work.