Yes, when you open a document in Underword, you can save it in the other format as well.
- While holding down the Option key, select File > Save As… or use the keyboart shortcut
- In the save panel, above the button row at the bottom, select the desired output format.
- Click Save. The new file is saved at the given location and the open document in Underword is automatically updated to point to the new location.