To find the visuals of your Board in your PDF Report, you need to capture them.
1 - From your Board
Display the area of the Board you wish to integrate into the report, then access the export menu (top right).
2 - Capture
Select the "snapshot"
The capture is made with a simple click and will be available in the gallery.
3 - Export report
Once you've made your captures, click on "pdf report".
A PDF document will be downloaded containing all the captures you've made.