I suppose that your test would do 3 steps:
- visit your target website, find links to PDF and Excel files
- download PDF and Excel files into local disk, rather than opening them in browser
- do whatever verification over the downloaded PDF/Excel files
You can implement the step1 using WebUI.* keywords. Also you can implement the step2 using WS.* keywords. You can mix WebUI.* and WS.* keyword together in a test case in Katalon Studio. The following discussion might help you:
The step3 is something new. Enjoy development!