MIT Gets Presentation Right : pdftk Tutorial

From the Edx course :

pdftk 1.pdf 2.pdf cat output 12.pdf	Merge the two documents 1.pdf and 2.pdf. The output will be saved to 12.pdf.
pdftk A=1.pdf cat A1-2 output new.pdf	Write only pages 1 and 2 of 1.pdf. The output will be saved to new.pdf.
pdftk A=1.pdf cat A1-endright output new.pdf	Rotate all pages of 1.pdf 90 degrees clockwise and save result in new.pdf.