To load a Nevron rich text document synchronously from a local file call the LoadFromLocalFile method of the rich text view. This method doesn't work on sandboxed platforms like Blazor WebAssembly.

richTextView.LoadFromLocalFile(@"D:\Documents\MyTextDocument.ntb");

To load a Nevron rich text document asynchronously call the LoadFromFileAsync method of the rich text view. Calling this method shows a loader over the rich text view until the loading completes. The method returns a promise, which can be used to get notified when the loading completes.

richTextView.LoadFromFileAsync(@"D:\Documents\MyTextDocument.ntb").Then(
    delegate (bool success)
    {
    },
    delegate (Exception ex)
    {
    }
);

To load a rich text document from a stream call the LoadFromStream method of the rich text view and pass the text format to load:

richTextView.LoadFromStream(stream, NTextFormat.NevronBinary);

The OpenFileAsync method shows an Open File dialog with all supported text formats:

richTextView.OpenFileAsync();

If you want a specific format to be selected by default, pass it as an argument:

richTextView.OpenFileAsync(NTextFormat.NevronBinary);