So Core accepts XPIF for jobs when the XPIF is submitted as a seperate file (.xpif) with the same name as the incoming print pdf.
So to use an pdf that already has an embedded (pre-pended) XPIF ticket, the ticket needs to be stripped off the pdf file and saved as a separate file with the name of the PDF to print. This can be done via a hotfolder with scripting.
I recommend you reach out to PSIS group for assistance with this as they have done this for other customers as a FEE BASED service which is why I cannot give it to you. But understand a few things - depending on what media etc is in the Fiery, not all attributes always make it through. The ticketing (like media) in the XPIF if it does not match what is loaded and available in the Fiery, then that information tends to get dropped.
Depending on how the XPIF ticket was built, often there is data or information in it that should be removed (incompatibilities with Fiery). This has to be defined and conversion tested.
Also, as a heads up, if you strip off the XPIF at the beginning of the file and then save the new pdf, make certain there are NO extra lines or carriage returns or line feeds at the beginning of the new pdf. Having ANY extra data at the beginning of the pdf file will cause the Fiery to CRASH immediatly upon receiving that incorrectly formed pdf file (I know this from experience). The incorrectly formed pdf will open with Acrobat just fine, but the Fiery wont like it.
