I have a pdf file which contains some three lines of text on the top of every page.  Is there any way to remove that 2cm horizontal strip from all pages of this pdf file using any command line tool.  I am using ubuntu. 
Remove a horizontal top strip on all pages of a pdf file
ubuntu;pdf
PDFjam should be able to do it. It should be installable on Ubuntu with sudo apt install pdfjam. Then, move into the directory containing your PDF files and run:for f in *pdf; do pdfjam --keepinfo --trim 2cm 0mm 0mm 0mm --clip true --suffix cropped $f; doneThat will create a cropped copy of each pdf file in the directory, where file.pdf becomes file-cropped.pdf. If you are satisfied those are correct, you can move them to a new directory (mv *-cropped.pdf newdir/) and delete the rest. 