How to reduce the size of a pdf file from command line

The 'pts' unit used by pdfinfo denotes a PostScript point. A PostScript point is defined in terms of an inch and a resolution of 72 dots per inch:

In the late 1980s to the 1990s, the traditional point was supplanted by the desktop publishing point (also called the PostScript point), which was defined as 72 points to the inch (1 point = 1⁄72 inches = 25.4⁄72 mm = 0.352¯7 mm [ ≙ 0.3528 mm] ).

The manual to gv contains a list of common paper formats specified in PostScript points.

You can use gs - GhostScript (PostScript and PDF language interpreter and previewer) as follows:

• Set pdfwrite as output device by -sDEVICE=pdfwrite

• Use the appropriate -dPDFSETTINGS.

  From Documentation:

  -dPDFSETTINGS=configuration
  Presets the "distiller parameters" to one of four predefined settings:
  

  • /screen selects low-resolution output similar to the Acrobat Distiller "Screen Optimized" setting.
  • /ebook selects medium-resolution output similar to the Acrobat Distiller "eBook" setting.
  • /printer selects output similar to the Acrobat Distiller "Print Optimized" setting.
  • /prepress selects output similar to Acrobat Distiller "Prepress Optimized" setting.
  • /default selects output intended to be useful across a wide variety of uses, possibly at the expense of a larger output file.

• -o option to output file which also set -dNOPAUSE and -dBATCH (see Interaction-related parameters)

Example:

$ du -h file.pdf 
27M file.pdf

$ gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -q -o output.pdf file.pdf

$ du -h output.pdf 
900K    output.pdf

Here -q suppress normal startup messages, and also do the equivalent of -dQUIET which suppresses routine information comments