Problem importing RAW files to Lightroom Mobile

Having imported and edited the RAW X3F files from my old Sigma SD15 on Lightroom Desktop (CC) I can then edit them on my iPad using Lightroom Mobile. However if I try and import the RAW files to my iPad the file format isn’t readable by Lightroom Mobile at the import stage.  As it works with the Desktop version what are the chances that the Mobile import setting can be changed to make it work?

{Moved from Lightroom Cloud to Lightroom Mobile Forum by Moderator}