Clicking on my mobile My Cloud Home/ Files/ Sync from desktop/ Documents/ gets to Office documents I recognize from my PC but with a an ending of .doc, .docx, .xlsx, .pps, .pst, .png, .ini, .one, .onetoc2, and these are “not supported” though my mobile supports Office files.
Such files require native tools or supported applications using which all of these files can be read. I would recommend to install native supported applications in mobile which can read these files formats.
