Mendix has built-in document generation functionality, that is somewhat limited but could be sufficient for your needs.
You can read up on it in the reference guide: https://docs.mendix.com/refguide/generate-document
You can create a document template, and in a microflow use that template to create a document that the user can download as a pdf.
My PrintScreen test project does print a scrollable portion of the screen. Please download the project to see how it works.
The PrintScreen widget uses a version (0.4.1) of the HTML2Canvas library that does not support downloading of off-page (so scrollbar needed) elements.
A newer beta version (0.5.0) of this HTML2Canvas library does cater for that, but is still in beta phase. So.. don't expect a fix anytime soon as related to the widget.