Paper notes are ingame source texts which provide (additional) information on certain subjects. Although they sometimes contain images, they mostly consist of text.
In Fallout 3 and Fallout: New Vegas, paper notes do not show up in your inventory. Instead, the notes are input directly into your Pip-Boy 3000 and can be read in the "Notes"("Misc" in New Vegas) category of the "Data" screen. The process is the same with the Fallout 4 Pip-Boy 3000 Mark IV and the Fallout 76 Pip-Boy 2000 Mk VI.