there is a mistake with the accessibility modifier for `Telerik.XamarinForms.RichTextEditor.RichTextPasteType`. When it is Internal it's not possible to use the PasteCommand since it requires that type as input.
Solution:
use reflection to get the enum
var assembly = typeof(RadRichTextEditor).Assembly;
var type = assembly.GetType("Telerik.XamarinForms.RichTextEditor.RichTextPasteType");
var obj = Enum.ToObject(type, 1);
await Clipboard.SetTextAsync("A pasted text");
var canExecute = richTextEditor.PasteCommand.CanExecute(obj);
richTextEditor.PasteCommand.Execute(obj);