This might be because the file you have uploaded is an older, non-Open XML file, such as a DOC, XLS, or PPT. These older file types cannot be viewed in the new document viewer. If this is the case, you must convert the file to Open XML (such as DOCX, XLSX, and PPTX) and then re-upload it using the Update content with a new file option, in the Edit content screen. For more information on how to do this, see Replacing older Microsoft files with open XML versions.