If this is for an RPA (an unattended process), I would simply suggest that you remove any PDF Viewers from the machine which should cause the file to simply download. You could then use any of the posts in the community about working with the Internet Explorer download bar.

If this is for an RDA (where you may not be able to remove the PDF Viewer), then it would get more complicated. You might start by looking at the Windows tab in the adapter to see if you can locate the save control there. If you can find it, and if you can call PerformClick on it, then that should work.

You might also try using the ClickByText or ClickByName methods. These methods use UI.Automation to click controls by their given name or by their text. You can use the Inspect.exe that comes with the Windows SDK to help locate these properties on a given control.