How can I darken the print on PDFs?
If you feel like the text on your PDF files is too light to make sense of or you’re just generally looking for your PDFs to have a darker print, you can make the suitable changes on Adobe Acrobat.
Go to Edit > Preferences > General
Here, under the Accessibility tab, check what the Document color option says and switch it to Black
Go to File > Print and click on the Advanced button. Check the Print as Image box and try if it prints in a darker color