To whom ever has the same problem in the future.
The end of this was as follow:
The config for the printing of the Purchase Order in SRM is done in transaction BBP_PO_ACTION_DEF.
With this transaction you can ONLY set a SMARTFORM and method to be triggered.
The BADI BBP_PROCESS_PO is supposed to allow you to change some stuff and maybe try and call a ADOBE form.
HOWEVER... when you select the print preview option the super SAP standard code totally bypass the method (PROCESS_BBP_PO_PRN) that was specified in BBP_PO_ACTION_DEF and a function module BBP_OUTPUT_PO_PREVIEW_SMART is called. The function module never calls the method (PROCESS_BBP_PO_PRN) or BADI implementation, which is called in (PROCESS_BBP_PO_PRN) so whatever you do in the BADI is pretty much useless Image may be NSFW.
Clik here to view.
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So in the end, I had to develop a new SMARTFORM with the customer layout that was linked in BBP_PO_ACTION_DEF delete the pretty Adobe form I developed Image may be NSFW.
Clik here to view..
And that is the best answer that I was able to come up with... and will therefore close this thread. Please feel free to add to this if you for some reason find and another solution.
