To view and download CAD/Revvit files in CaterQuotes, you'll first need to make sure that they are showing in the catalogue.
First go to the catalogue, then above the details panel (on the right) there is an "Edit" button. Click on this and you will be shown a list of panels.
Tick the boxes next to CAD and Revvit. If the item has these files attached, you will be able to see them in the details panel.
To download a file, just single click on it and choose where to save it.