As usual, not going to write too much here but give you exactly what you need.
To rotate the first page from a pdf 90 degrees clockwise:
$ pdftk in.pdf cat 1E output out.pdf
To rotate all pages from a pdf 90 degrees clockwise:
$ pdftk in.pdf cat 1-endE output out.pdf
To rotate all pages from a pdf 90 degrees counter clockwise:
$ pdftk in.pdf cat 1-endL output out.pdf
The E is meaningful. 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.
END?
