The option in Backstage view that contains the command to change the file type of a saved file is Export.

In Microsoft Office applications that use Backstage view (like Word or PowerPoint), the Export section is where you find commands such as “Change File Type,” “Create PDF/XPS,” or other format-conversion tools, all focused on saving the existing file in a different format. Options like New , Info , or Publish relate to creating files, viewing document details, or sharing/publishing, but they do not house the command specifically used to change a saved file’s type.