How to compress scanned PDF?

One problem with scanned pdfs is that the size is so bloated. One good solution to compress such files is this one script:

#!/bin/sh

gs  -q -dNOPAUSE -dBATCH -dSAFER \
    -sDEVICE=pdfwrite \
    -dCompatibilityLevel=1.3 \
    -dPDFSETTINGS=/screen \
    -dEmbedAllFonts=true \
    -dSubsetFonts=true \
    -dColorImageDownsampleType=/Bicubic \
    -dColorImageResolution=120 \
    -dGrayImageDownsampleType=/Bicubic \
    -dGrayImageResolution=72 \
    -dMonoImageDownsampleType=/Bicubic \
    -dMonoImageResolution=120 \
    -sOutputFile=out.pdf \
     $1


Here the compression rate can be changed by tweaking resolution values. I found the above gives a good compression without sacrificing the text quality.

PDF join files and replace strings using pdftk

pdftk *.pdf cat output combined.pdf

 ===========

You can try to modify content of your PDF as follows

1. Uncompress the text streams of PDF

   pdftk file.pdf output uncompressed.pdf uncompress

2. Use sed to replace your text with another

   sed -e "s/ORIGINALSTRING/NEWSTRING/g" <uncompressed.pdf >modified.pdf

3. If this attempt was successful, re-compress the PDF with pdftk

   pdftk modified.pdf output recompressed.pdf compress

Sources:
https://www.pdflabs.com/docs/pdftk-cli-examples/
http://stackoverflow.com/a/9872494/4151875