pdf shrink compress file in ubuntu

1. sudo apt-get install texlive-extra-utils

2. pdfcrop --margins '0 0 0 -25' --clip input.pdf output1.pdf
3. pdfcrop --margins '0 0 0 25' --clip output1.pdf output2.pdf
4. gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.7 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output3.pdf output2.pdf