This tool cuts a rectangular area on every page of PDF, and saves result to the new document. You just need to specify the coordinates of the rectangle, its width and height.
Go to the "Operations" section of the program, and choose "Crop Pages" item. If you want to process all pages, choose the "Process all pages" option. If you want to process specific pages, choose the second option, and enter the page range.
For example: 1, 2, 6-8.
Then choose the position and size of the crop box. Remember, the default Units are pixels, but you can change the Page Units option on the "Settings" section of the program.
When ready, click the "Crop" button to start the process.