gistfile1.txt

# Resources\xml\provider_paths.xml
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-files-path name="reports" path="Reports" />
</paths>


# Add it to your manifest in application section 

<provider android:name="androidx.core.content.FileProvider" android:authorities="ch.xxx.xxxx.provider" android:exported="false" android:grantUriPermissions="true">
			<meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/provider_paths" />
</provider>


# Open file method

        public void OpenFile(string filePath)
        {
            try
            {
                string extension = Path.GetExtension(filePath);

                string application;
                switch (extension.ToLower())
                {
                    case ".doc":
                    case ".docx":
                        application = "application/msword";
                        break;
                    case ".pdf":
                        application = "application/pdf";
                        break;
                    case ".xls":
                    case ".xlsx":
                        application = "application/vnd.ms-excel";
                        break;
                    case ".jpg":
                    case ".jpeg":
                    case ".png":
                        application = "image/jpeg";
                        break;
                    default:
                        application = "*/*";
                        break;
                }

                Java.IO.File file = new(filePath);
                file.SetReadable(true);
                # Important !
                Android.Net.Uri uri = FileProvider.GetUriForFile(Android.App.Application.Context, "ch.xxxx.xxx.provider", file);
                Intent intent = new(Intent.ActionView);
                intent.SetDataAndType(uri, application);
                intent.AddFlags(ActivityFlags.NewTask);
                intent.AddFlags(ActivityFlags.GrantReadUriPermission);
                Android.App.Application.Context.StartActivity(intent);
            }
            catch (Exception ex)
            {
                CrossToastPopUp.Current.ShowToastWarning(ex.ToString());
            }
        }
        

  # Method called to download and open

  string filePath = Android.App.Application.Context.GetExternalFilesDir("Reports").AbsolutePath + "/" + filename;
          File.WriteAllBytes(filePath, bytes);
          OpenFile(filePath);