The data sent to FormTrap in Print Line mode is unchanged from the original application. Unlike Records mode, the purpose of Print Line mode is to extract data from a print stream as it is generated by the application. FormTrap achieves this by mapping areas of the print stream data for print line extraction.

Print line extraction is the process of identifying fields in the print line data and linking them to the field names allocated to variable text objects on the form. Data is identified according to its position on a page in the print stream and linked to the form by highlighting areas of sample text. This is called print mapping.