By 'deskew', do you mean rotate? If the PDF document is a scanned copy, you can use 'Rotate Pages' under 'Organize' menu to rotate. If I misunderstand anything here, please feel free to correct me. Thank you.
You could rotate it with small degrees by going to Edit->Touch up->Touchup object tool, then click on the page and right click it->shear selected objects and input the number you need to rotate it.
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