Example how copy text to clipboard in Xamarin.Forms applications. - http://julianocustodio.com/clipboard

MainPage.xaml.cs

using Plugin.Clipboard;
using System;
using Xamarin.Forms;

namespace ClipboardDemo
{
	public partial class MainPage : ContentPage
	{
		public MainPage()
		{
			InitializeComponent();
		}

                private async void Copy(object sender, EventArgs e)
                {
                        CrossClipboard.Current.SetText(Mensagem.Text);
            
                        await DisplayAlert("Atenção", "O Texto \"" 
                                           + CrossClipboard.Current.GetText() 
                                           + "\" foi copiado.", "OK");
                }
         }
}