sudo apt-get install pdftk
To rotate page 1 by 90 degrees clockwise:
pdftk in.pdf cat 1E output out.pdf
To rotate all pages clockwise:
pdftk in.pdf cat 1-endE output out.pdf
The page rotation setting can cause pdftk to rotate pages and documents. Each option sets the page rotation as follows (in degrees): N: 0, E: 90, S: 180, W: 270, L: -90, R: +90, D: +180. L, R, and D make relative adjustments to a page's rotation.
Unabashedly stolen from here.