To rotate page 1 by 90 degrees clockwise:
pdftk in.pdf cat 1E output out.pdf # old pdftk
pdftk in.pdf cat 1east output out.pdf # new pdftk
To rotate all pages clockwise:
pdftk in.pdf cat 1-endE output out.pdf # old pdftk
pdftk in.pdf cat 1-endeast output out.pdf # new pdftk
Similarly, to rotate all pages anti-clockwise:
pdftk in.pdf cat 1-endwest output out.pdf