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. Most print streams with more than one simple detail line should have been run through the Repaginator first, to remove redundant lines and to move total lines behind the Header (they can then be treated as part of the header). These steps simplify Print Line form design as well as allowing use of some of the advanced features.

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.