Currently the PDF generation is based on the desktop layout. There is no way to have a field on the PDF view that is not on the desktop layout. It would extremely helpfull if there was a separated layout (PDF Layout), so the controls can be rearranged as needed.
An eventual implementation would be quite straight forward as all it is necessary is to add a new "desktop layout" to the designer and call it PDF layout. Then the PDF generator would be based on the new layout instead of the desktop layout.
Ruslan Urban commented
It would be great if PDF generation would apply print-mode CSS classes and form rules to have the ability to hide or show controls in the printable layout (e.g. buttons or panels with legal/information sections). That would eliminate the need to create a new form layout if all you want is to hide a few controls.
Another great feature would be to add a button with action "Print" that would generate a printable HTML view of the form where all SharePoint page chrome is stripped off and print-mode CSS classes and media queries are applied to form controls (see https://community.nintex.com/community/build-your-own/blog/2017/09/11/print-friendly-nintex-forms). That would save lots of effort implementing a workaround for printing when you need it on multiple forms.