When you call openURL an external program should be opened. The issue you are facing is probably the result from the ULC UX not be able to run other programs from your server.
What you could do is to open your PDF URL with an HTML link from a webview EWO and set the property ulcClientSideWidget to true.
Its a bit hard to explain, I have tried something similar last week. See attached example. Just take a look a the files and adapt them to your needs.
I have a similar problem, I just need to open new tab from ULC UX. I tried this solution with loading html page in webview that opens new tab on click, but when i set the property ulcClientSideWidget on true, the page does not load in ULC UX (it loads when i start panel directly in WINCC OA) and when i set the property to false, the page loads, but nothing happens on click. Any ideas?
I am also facing same problem, I want to open new tab from ulc ux.
when i set ulcClientSideWidget to false, html page loads in webview in ulx ux (refer attached snapshot), but nothing happen in both (ulc ux and server UI) on clicking link. When i set ulcClientSideWidget to true, html page doesn't load in webview in ulc ux.
Pls suggest.