I am using ActivityResultContracts.OpenDocument() to open a PDF. I get its uri.
But how can I load it into a webView component? I'm using SDK 33.
You don't. It's a webview, it displays HTML, not PDF. It doesn't have a PDF viewing mode. There are some hacks out there where you upload the file to google docs or similar sites then open a webview to that site, but the webview won't be able to display a local pdf.