You can exclude controls (fields) from the autogenerated PDFs that Orbeon produces.
This script hides (excludes) the control from the autogenerated PDF output.
fr:mode() != 'pdf'
TIP: You can 'inverse' this script (fr:mode() = 'pdf') for the opposite effect. You can use this to show a control on the PDF but not on the form. This could be useful for things like providing feedback to knowledge tests, compiled address blocks, etc.
You can also use this to create a "double-form" that contains the controls presented in one way to the user, and another way in the PDF. This effectively means you are creating two 'versions' of the form, one above the other. The 'first' form presents the controls in a vertical format for ease of the user, while the 'second' lays the data collected from the user in an easier to read or print traditional pattern.
TIP: You can also apply this script at the Section level to hide the section and all its controls from the PDF. This can save you time and effort, and will remove the section heading from the PDF as well.