To get started open a PDF in Acrobat X on your computer.
Step 1: Creating a CropBox
With the document open in Acrobat X, go to the Pages panel, and select Crop.
On the document, draw a rectangle of the area you wish to crop.
Once this is done you may move, or resize the CropBox as you wish.
Step 2: Cropping
To do this, double click on the CropBox you created in the previous step.
This will open the Set Page Boxes dialog.
You may adjust Top, Left, Bottom, and Right to further adjust the CropBox.
Also, you may select which pages you wish to select by adjusting page ranges.
Finally, press OK to crop the selected pages, to the CropBox.