Thank you for using our product. We apologize for not stating it in the Manual PDF.

To insert an underline  :
Insert a space in where you would like to add an underline. Then select the space area and click “underline key” in the software. You can add a longer underline by selecting a longer space area.

In this software, space area is recognized as a letter. Inserting a space in advance will allow you to add an underline.