Free Editor, as you can gather from the name, is completely free to use, and according to its support pages, can open and edit 75 different file types, including Microsoft Office files, other ...

Use the free PSD Viewer for Photoshop to open these files on iOS. For Illustrator AI files, grab the free doctape viewer app, which is a cloud service that actually converts the file to a PDF for ...

Next, right-click on any file that’s in a non-Google Drive format, such as an Excel spreadsheet, Word document, or photo and select Open with from the contextual menu.

If you cannot open an Excel file and see Excel cannot open the file because the file format or extension is not valid error, see this post.