Here is how you can find solution by yourself:
- Start Excel
- Press Alt+F11 to start Microsoft Visual Basic
- Press F2 to start Object Browser
- Enter "SaveAs" in Search Text box and press Enter to search for this method
- Select any SaveAs method for class Workbook in the search results to get it params
- As you see it need FileFormat so enter this text in the Search Text box and press Enter
- Select XlFileFormat and get complete list of all avaiable formats