@itsfoss >It's "FOSS". >3 of the pdf videos recommended are proprietary malware "PDFsam Enhanced" and "PDFsam Visual" are proprietary malware (read these https://pdfsam.org/pdfsam-enhanced/eula/https://pdfsam.org/pdfsam-visual/eula/ if you doubt my word - if the "EULA" forbids reverse engineering, there is a 100% chance the software contains malware that the author doesn't want you to reverse engineer clearly), but of course they didn't write that, just that those are "paid".
Of course GNU Ghostscript and mupdf aren't mentioned either.