• Case-insensitive search of a string in a PDF, thanks to pdfgrep  : 

    1$ pdfgrep --page-number --ignore-case 'my_string' ./document.pdf

  • Convert a PDF to a JPEG file at 150 dpi: 

    1$ convert -density 150 ./document.pdf ./document.jpg

  • Extract images from a PDF document: 

    1$ pdfimages -j document.pdf prefix

  • Compile all JPEG files in the current folder into a single PDF at 150 dpi: 

    1$ convert -density 150 ./*.jpg ./document.pdf

  • Remove password of a PDF: 

    1$ pdftk ./password-protected.pdf input_pw PROMPT output ./no-password.pdf

  • Split a PDF into pages: 

    1$ pdftk doc.pdf burst

  • Merge 2 PDF documents: 

    1$ pdftk doc1.pdf doc2.pdf cat output newdoc.pdf

  • Same as above, but for all PDFs of the current folder. This also have the nice side effect of removing all DRMs :) : 

    1$ gs -sDEVICE=pdfwrite -dBATCH -dNOPAUSE -q -sOutputFile=bigfile.pdf ./*

  • Reduce size of PDF (see GhostScript -dPDFSETTINGS documentation  ): 

    1$ gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -q -o small-output.pdf large-input.pdf

  • Reduce a big.pdf file to a smaller.pdf file by limiting its images to 1000 pixels and convert them to grayscale: 

    1$ pdfimages -j ./big.pdf prefix
2$ convert -resize 1000x1000 -type Grayscale -density 150 ./prefix-*.jpg ./smaller.pdf
3$ rm prefix-*.jpg

Additional References