#Linux One-liners to manage pdf documents

Set a black background with ImageMagick: a brute‑force method that rasterizes the vector and significantly increases file size.
convert -density 300 input_white.pdf -background black -negate output_dark.pdf

Merge many .jpg files into one pdf
convert *.jpg doc.pdf

Set a password
pdftk file.pdf output file_pw.pdf userpw PROMPT

UnSet a password (two options)
pdftk file_pw.pdf output file.pdf user_pw MYPASSWD
qpdf --password=MYPASSWD --decrypt crypt.pdf de_crypt.pdf

Remove pages
pdftk old.pdf cat 1-9 15-end output new.pdf

Merge many docs
pdftk 1.pdf 2.pdf 3.pdf cat output 123.pdf

Reduce doc size

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH ->sOutputFile=output.pdf input.pdf

_{The option /screen defines the most quality degree and size reduction factor.
Here the complete list of options from low to high quality: /screen, /default, /ebook, /printer, /prepress.}

please feel free to write comments suggestions and alternatives

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