Preview for Mac: Crop or rotate a PDF in Preview
You can crop a page to hide content, or rotate it to change its orientation.
Crop a PDF
To crop a PDF, you first select the area you want to keep, and then discard the rest. If you want to view the dimensions of the content you’re selecting, choose Tools > Show Inspector, then click the Crop Inspector button 
and choose a unit of measurement that’s displayed in the Crop Inspector window.
If the Markup toolbar isn’t showing, click the Show Markup Toolbar button
, then click the Rectangular Selection button 
.Select the portion of the page you want to keep.
Click the Crop button in the Markup toolbar.
Note: To undo the crop immediately, choose Edit > Undo Crop. To undo the crop later, return to a version before the crop. Choose File > Revert To > Browse All Versions, then browse the versions to restore the one you want.
Rotate a PDF
Rotate one page: Click the Rotate button
. You can also choose Tools > Rotate Left or Tools > Rotate Right.Rotate several pages at once: Choose View > Thumbnails or View > Contact Sheet, select the pages to rotate, then click the Rotate button
.