====== PDF ======

===== Reduce size =====

    gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/printer -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf my_output.pdf

===== all jpg into one pdf =====

    img2pdf *.jp* --output combined.pdf