Can we modify or Edit the $po_receive page.
Unfortunately, $po_receive.do is an angular page that is being rendered from the backend so we cannot edit it.
The $po_receive.do is an angular page that is being rendered from the backend and that is the reason it is not available in any UI pages or UI macro.
But there is a UI page named "receive_order" which has the same functionality as $po_receive.do. The reason for having a separate UI page "receive_order" is due to support the IE browsers. Since IE browsers do not have complete support for the angular page, we would render the UI page named "receive_order" (we could see that there will be two UI actions named "Receive order" in the "proc_po" table, if we check the conditions, one UI action would be displayed for IE browsers where it would call the UI page "receive_order" and the other one (for all other browsers) would call the angular page $po_receive.do)
For making customizations one can copy the UI page "receive_order" and make the necessary customizations and then make the UI action "Receive order" call the customized UI page instead of the $po_receive.do.