To add a file or attachment to an event in your Microsoft Calendar:

1. Open the Microsoft Calendar app with your Outlook account
2. Select the event that you would like to add a file to
3. Click the ‘…’ icon in the upper-right corner of the event window
4. Select ‘Add File’ from the dropdown list
5. The 'add attachment' dropdown will prompt you to access files from your device
6. Select the file you'd like to add from your device
7. The file should be automatically added to the event
8. If necessary, edit the file name to suit the event