Make a pdf look scanned using ImageMagick

scanner.sh

# use ImageMagick convert
# the order is important. the density argument applies to input.pdf and resize and rotate to output.pdf
convert -density 90 input.pdf -rotate 0.5 -attenuate 0.2 +noise Multiplicative -colorspace Gray output.pdf

For those on Windows make sure to install Ghostscript as well or else you'll get errors like

convert: FailedToExecuteCommand `"gswin32c.exe" -q -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pngalpha" -dTextAlphaBits=4 -dGraphicsAlphaBits=4 "-r150x150"  "-sOutputFile=C:/Users/TURKEY~1/AppData/Local/Temp/magick-9420wtSmlrXSBcfh%d" "-fC:/Users/TURKEY~1/AppData/Local/Temp/magick-9420IJ2RKxHzcTQf" "-fC:/Users/TURKEY~1/AppData/Local/Temp/magick-9420t7VINjcK97Pq"' (The system cannot find the file specified.
) @ error/delegate.c/ExternalDelegateCommand/475.
convert: PDFDelegateFailed `The system cannot find the file specified.
' @ error/pdf.c/ReadPDFImage/662.

thank you! I have used some of these commands to build https://oakpdf.com which not only applies scanner effect, but also allows to insert an image of signature or draw a signature.
My observations regarding -density parameter: 200 is good enough in most cases, while 300 gives ultimate quality - but the build time get catastrophically slow..

Great

Thank you!
I used zenity to add graphical input and output prompts:
convert -density 150 "$(zenity --file-selection --title="Select Input File" --file-filter=*[PpDdFf])" -rotate "$([ $((RANDOM % 2)) -eq 1 ] && echo -)0.$(($RANDOM % 4 + 5))" -attenuate 0.4 +noise Multiplicative -attenuate 0.03 +noise Multiplicative -sharpen 0x1.0 -colorspace Gray "$(zenity --file-selection --save --title="Select Output File" --filename ".pdf")"

Can also be found here as a .desktop file, so the script can be started from the starter on Linux machines:
https://gist.github.com/fewaltix/c1437171d16671741aafe146751dbf9f

work