Installation Imagemagick
https://imagemagick.org/script/download.php
make PDF like scanned copy (after adding e-signature)
convert -density 300 input.pdf -attenuate 0.45 -sharpen 0x1.0 -rotate 0.4 output.pdf
additional parameters
-colorspace gray
-blur 0x1
-quality 85
-compress JPEG
Merge images or PDFs
convert +append *.png merged.png
convert -append *.pdf merged.pdf
-append : one after the other +append : side by side
Export PDF as an Image
convert file-?.pdf file.jpg
Reduce scanned PDF size
convert -density 200x200 -quality 60 -compress jpeg input.pdf output.pdf
or
convert -density 150x150 -compress Zip input.pdf output.pdf
or
convert input.pdf -resample 85% output.pdf
References
https://askubuntu.com/questions/113544/how-can-i-reduce-the-file-size-of-a-scanned-pdf-file
https://gist.github.com/bre7/468e4a73bc7a6b5ae5542c2529fc58a3
https://gist.github.com/scf37/39e2724e7e091ed2a9bc75532244a832