I am using Acrobat 9. In previous versions of Acrobat I could rotate a scanned image in the PDF Optimizer so that horizontal lines were parallel to the top and bottom of the page. This function doesn't seem to be available any longer; the only rotations are 90 or 180 degrees.
Open a PDF containing a scanned image.
Reduce the page zoom to something between 70 & 60 percent (just for ease of viewing the full page).Bring up the TouchUp Object Tool.
Starting just outside one corner of the page click and drag to select the entire page.
Should see a series of boxes that represent XObjects that hold the parts of the image.
With the mouse cursor somewhere "on" the page, right click for the context menu.
You want to click on "Rotate Selection".
Now, position the mouse cursor precisely on the "dot" that appears at each of the four corners.
You want the cursor icon to become a diagonal line that is bisected by another, short line and having an arrow head at each end of the diagonal line.
Note, the diagonal line needs to be displayed tangential to the point. If an arrow head points "into" the box you'll be able to shrink/expand the box in focus; but, not rotate.
So, once you've that tangential appearance left click and move the mouse left, right, in a circular motion. Grin while the box spins.
Alternatively, you can just select a single XObject and spin that piece of the image set that's been painted to the PDF.
8^)
Be well...