Hello,
You are correct in that you need to create a new screen for this. For the screen, you would need to create a new tab so you can set user permissions. The permissions would allow certain users to see the read-only screen and not the editable invoice screen.
For the screen itself, you need to make any field and grid read-only. Also, you will have to make sure buttons like Save are off or inactivated.
You will find the read-only checkbox on Step one of the field setup menu.
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For grids, you will find the read-only option under the Advanced options for the grid.
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I'm hoping this helps. Let me know if you need any more guidance or have any more questions.
Greg