NuGet Package: https://www.nuget.org/packages/Xamarin.Forms.SaveOpenPDFPackage/

1. Download this Package just in your Standard Library.
2. Platform specific things:

Android:

In the AndroidManifest.xml file, you have to add theese lines:

https://github.com/officialdoniald/Xamarin.Forms.Save.Open.PDF/blob/master/Xamarin.Forms.Save.Open.PDF/Xamarin.Forms.Save.Open.PDF.Android/Properties/AndroidManifest.xml

Create, if you don't create yet, an "xml" folder into the "Resources" folder in the Android Project, and create an xml file, and call it: "provider_paths.xml". The file should contain: https://github.com/officialdoniald/Xamarin.Forms.Save.Open.PDF/blob/master/Xamarin.Forms.Save.Open.PDF/Xamarin.Forms.Save.Open.PDF.Android/Resources/xml/provider_paths.xml

Android ready, let's go to iOS.

iOS:

Don't need any nessessary thing.

3. Use the packge's function:

await CrossXamarinFormsSaveOpenPDFPackage.Current.SaveAndView(Guid.NewGuid() + ".pdf", "application/pdf", stream, PDFOpenContext.InApp); // if you want to open the PDF in your app

await CrossXamarinFormsSaveOpenPDFPackage.Current.SaveAndView(Guid.NewGuid() + ".pdf", "application/pdf", stream, PDFOpenContext.ChooseApp); // if you want to open the PDF outside the app

First parameter: Guid.NewGuid() + ".pdf" -> I created a unique name for the pdf file, but you can change it to whatever you want Second parameter: a stream (System.IO.Stream), so you need to download or open an existing pdf, the point is that you have to convert your pdf into a stream Third parameter: how you want to open your pdf