pmiller2 linked[0] to some alternatives[1], including this one[2] which only requires ImageMagick:
convert letter.pdf -colorspace gray \( +clone -blur 0x1 \) +swap -compose divide -composite -linear-stretch 5%x0% -rotate 1.5 as-scanned.pdf
[0] https://news.ycombinator.com/item?id=23157979
[1] https://tex.stackexchange.com/questions/94523/simulate-a-sca...