I was avid TTRPG DM and Player, this means I have a plenty of rulebooks from different systems. Most of them in PDF and they are horrible in size. I don't want to use online services and most of services have a limits on size or quantity of pdf for processing.

"Scratch my own itch" approach leads to create pdfslim. Offline tool for pdf compression and optimization. Allows bulk-processing, memory tweaking and sufficient level of compression (HtR from 145 Mb to 10 Mb for example).