Coordinate system error when attempting to switch to a GeoPDF basemap in an offline map

[BradyCallahan]

I'm getting a "Basemap Unavailable - The spatial reference isn't compatible with this map" error when attempting to switch to a GeoPDF basemap in an offline Map.

I created three GeoPDFs in Pro, all at the same time, and side-loaded them to the Basemap folder on my device. They all show up in the Basemap Gallery in Field Maps and work fine in dynamic maps. However, if I attempt to pick one while using an offline map I get that spatial reference error.

I made sure that the Map SRS in Pro was set to WKID:3857 before exporting the GeoPDFs. However, one oddity is that when I brought them back in to Pro, their WKIDs are listed as the outdated Web Mercator tag of WKID:3785.

Anyone else seeing these types of issues or got any ideas?

iOS 26.3.1
Field Maps 26.1.1
ArcPro 3.5

[BradyCallahan]

Not exaclty sure what you mean about browsing for the item in my org. 

If I upload the PDF to AGOL and make it available to Field Maps there doesn't appear to be a way to have that PDF available as a basemap on the device unless I lock a Web map to it. I can do that however, and when I go offline, the PDF gets downloaded as the basemap. The issue though is that there's no way to change the basemap to a different PDF without running into the error. 

Just got the notice below

BUG-000183698 has been closed: As Designed.

This is as designed, it is a workaround related to the limitations of Adobe products. The Esri Projection Engine included in Adobe Acrobat is an older version that does not support Web Mercator (EPSG 3857). In order to provide any georeference information in exported PDFs using Web Mercator, we write an older EPSG code that is properly supported by the projection engine version included in Adobe products. If at some future juncture Adobe updates their copy of the projection engine, we could modify PDF export to write the newer Web Mercator Auxiliary Sphere.

[JonathanLebowitz]

I guess my question was essentially if you were able to download it from ArcGIS Online and open it up in Field Maps without an error message. I will need to investigate if the Field Maps team is aware of this limitation since Esri basemaps are defined in WGS 84 Web Mercator.

[BradyCallahan]

Defect #: ENH-000184814

Synopsis: Enable native support for EPSG:3785 georeferenced PDFs in ArcGIS Field Maps to ensure basemap compatibility with ArcGIS Pro layout exports