With the gs command it is possilbe. 'gs' stands for Ghostcript (PostScript and PDF language interpreter and previewer).
gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=settings -sOutputFile=output.pdf input.pdf
Whereas possible options for PDFSETTINGS are:
- /screen
- - lowest resolution and file size, fine for viewing on screen
- /ebook
- - middle was of resolution and file size
- /printer
- - for printing it
- /prepress
- - for highquality printing(?)
Source for this:
https://www.techwalla.com/articles/how-to-make-the-output-darker-on-a-pdf-print