To crop PDF pages, open your PDF file. Click the Crop page button on the Edit tab, or click Edit > Crop page on the menu. The Crop pages dialog will appear. On the left side, drag the rectangle's handles to change the size of the cropped area.

Crop Margin
You can also type in directly into the crop margin entry fields at the right side of the dialog. You can change the default unit by going to the Options on the toolbar.

Crop Page
Select All to crop every page
Select Custom to select a specific page to crop by entering the page numbers on the textbox below the dropdown.