I've seen a lot of questions on how in Android to view a PDF that was downloaded by the app.
Here's an easy solution I found that works for me. My app downloads report pdfs and need to show them.
Basically you copy the file from the private storage to the external storage. That's it.
//Read all the PDF data from the LOCAL PRIVATE STORAGE where you saved it to
//PathToFile is just a function that gets the path I wrote
var bytes = File.ReadAllBytes(PathToFile(fileNameofPrivateFile));
//Copy the private file's data to the EXTERNAL PUBLIC location
var externalPath = global::Android.OS.Environment.ExternalStorageDirectory.Path + "/report.pdf";
File.WriteAllBytes(externalPath, bytes);
//Open it up
Uri pdfPath = Uri.Parse(externalPath);
Intent intent = new Intent(Intent.ActionView);
intent.SetDataAndType(pdfPath, "application/pdf");
intent.SetFlags(ActivityFlags.NewTask);
Forms.Context.StartActivity(intent);