Google has made it possible to directly edit, comment, and collaborate on Office files using Google Docs, Sheets, and Slides without converting the Office file to a Google file first. All changes made to Office files later than Office 2007 in Google are auto-saved to the file in their original Office format. 

You can use Office editing with:

• Word files: .doc, .docx, .dot
• Excel files: .xls, .xlsx, .xlsm, (macro enabled Excel files), .xlt 
• PowerPoint files: .ppt, .pptx, .pps, .pot 

To learn more about what you can do with Office files in Google, visit the Google Drive Help Center.