When exporting a map layout with a transparent background to a PDF file in ArcGIS Pro, the background transparency is not honored.

Workaround

Export the layout to an Adobe Illustrator Exchange (AIX) file, with the ‘Keep layout background’ option unchecked, and import it into Maps for Adobe Creative Cloud/Illustrator. Export it to a PDF file from there. Refer to the following link for more information regarding the 'Keep layout background' option: https://pro.arcgis.com/en/pro-app/latest/help/sharing/overview/aix-export.htm

Steps to Reproduce