Как открыть pdf удаленного пути в webview xamarin.forms

Необходимо использовать службу зависимостей Xamarin. Вот как я это сделал.

Сначала определите интерфейс:

namespace Mobile.DependencyService
{
    /// <summary>
    /// 
    /// </summary>
    public interface IDownload
    {
        /// <summary>
        /// 
        /// </summary>
        /// <param name="name"></param>
        /// <param name="bytes"></param>
        /// <param name="fullPathToSavedFile"></param>
        void Save(string name, byte[] bytes, out string fullPathToSavedFile);
    }
}

Внутри вашего события клика: var uri = ваша ссылка на pdf;

var uri = repository.GetResumeUri(model);

  if (Device.OS == TargetPlatform.Android)
  {
    using (var clientHandler = new System.Net.Http.HttpClientHandler())
    {
       using (var httpClient = new System.Net.Http.HttpClient(clientHandler))
       {
           httpClient.BaseAddress = uri;
           byte[] bytes = await httpClient.GetByteArrayAsync(uri);
           var service = Xamarin.Forms.DependencyService.Get<Mobile.DependencyService.IDownload>();

           string fullPathToSavedFile;
           service.Save(
                        String.Format("{0}.pdf", System.Guid.NewGuid().ToString("N")), //String.Format("{0} Resume.pdf", model.Type),
                         bytes,
                         out fullPathToSavedFile
                         );

           uri = new Uri(String.Format("file://{0}", fullPathToSavedFile));
        }
     }
  }
  Device.OpenUri(uri);

В iOS:

[assembly: Xamarin.Forms.Dependency(typeof(Mobile.iOS.DependencyService.Download))]
namespace Mobile.iOS.DependencyService
{
    public class Download : IDownload
    {
      public void Save(string name, byte[] bytes, out string fullPathToSavedFile)
        {
            fullPathToSavedFile = String.Empty;

            try
            {
             fullPathToSavedFile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), name);

                File.WriteAllBytes(fullPathToSavedFile, bytes);
            }
            catch (Exception ex)
            {
                var ex1 = ex;
            }
        }
    }
}

Для Android:

[assembly: Xamarin.Forms.Dependency(typeof(Mobile.Droid.DependencyService.Download))]
namespace Mobile.Droid.DependencyService
{
   public class Download : IDownload
    {
       public void Save(string name, byte[] bytes, out string fullPathToSavedFile)
        {
            fullPathToSavedFile = String.Empty;
            // https://developer.xamarin.com/api/type/System.Environment+SpecialFolder/
            // http://developer.android.com/guide/topics/data/data-storage.html

            try
            {

                //var path = Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal), name);
                using(var directory = Android.OS.Environment.GetExternalStoragePublicDirectory(Android.OS.Environment.DirectoryDownloads))
                {
                    if (null != directory) 
                    {
                        var state = Android.OS.Environment.GetExternalStorageState(directory);

                        if (String.Compare(state, Android.OS.Environment.MediaMounted,true)==0)
                        {
                            fullPathToSavedFile = Path.Combine(directory.AbsolutePath, name);
                            File.WriteAllBytes(fullPathToSavedFile, bytes);

                            //File.WriteAllBytes(Path.Combine(directory.AbsolutePath, name), bytes);
                        }
                    }
                }
            }
            catch(Exception ex)
            {
                var ex1 = ex;
            }
         }
       }
     }