It is interesting that we can manipulate pdf file, especially pdf with many pages. Let’s say I want to extract certain page of it or combine two pdf files. So, here are the list of commands that I used to use in my daily job.
#pdftk original.pdf cat 1 3 20-35 50 output final.pdf
It means I extract page 1, 3, 20 until 35, and page 50 to a new pdf file.
$pdfunite 1.pdf 2.pdf 3.pdf final.pdf
It means I combined file 1.pdf, 2.pdf, 3.pdf into final.pdf. The page is in file order.