Most PDF Viewers come with the ability to print, email, text etc the PDF that is loaded.  For example, in the default iOS PDF viewer there is a "share" icon.  When the "share" icon is tapped, multiple options and apps come up that allow users to "print", "message/text", "email" the PDF.  It would be a great feature to have in the Xamarin UI PDF Viewer.  It could just be part of the PDFViewer Toolbar options.

The linear gradient brush in not displayed on some elements.

On images the gradient is visualized.

Zooming on physical devices does not work properly (gets stuck). Same behavior when scrolling and panning the document 

When trying to scroll, pan, and zoom, these gestures open the flyout menu, not to the document in the viewer.

The pdf content is not visualized properly on UWP and iOS when the file is loaded from a stream. 

Also if you try to load PDF twice on the same PDF Viewer, an exception is raised.

If you download the pdf document from the internet, save it to the device and try to show it inside PdfViewer, it will not be loaded on Xiaomi phones with MIUI 12.1. and above.

Users report similar issues with downloaded files on MIUI devices, here are a few discussions on the matter:

https://www.reddit.com/r/Xiaomi/comments/l3x5db/miui_12130_broke_file_permissions_on_mi10_lite/

https://www.reddit.com/r/Xiaomi/comments/mx05ur/file_downloading_issues_on_my_xiaomi/

It seems that's the same reason for the PdfViewer not showing downloaded pdf files as it properly shows pdf documents added as embedded resource to the solution.

System.MissingFieldException: Field not found: Telerik.XamarinForms.SkiaSharp.SkiaDocumentView.purePainter Due to: Could not parse field signature 0a00031b due to: Could not resolve type with token 0100014e from typeref (expected class 'Telerik.XamarinForms.SkiaSharp.DocumentView.SkiaDocumentPurePainter' in assembly 'Telerik.XamarinForms.SkiaSharp, Version=2020.3.1106.460, Culture=neutral, PublicKeyToken=null') assembly:Telerik.XamarinForms.SkiaSharp, Version=2020.3.1106.460, Culture=neutral, PublicKeyToken=null type:Telerik.XamarinForms.SkiaSharp.DocumentView.SkiaDocumentPurePainter member:(null)
  at Telerik.XamarinForms.PdfViewer.RadPdfViewer.UpdatePresenter () [0x00037] in <bd15b7ab3df742a5908d5d151a9a58d8>:0
  at Telerik.XamarinForms.PdfViewer.RadPdfViewer..ctor () [0x00048] in <bd15b7ab3df742a5908d5d151a9a58d8>:0
  at OnaMobile.Views.PdfViewPage.InitializeComponent () [0x00012] in C:\Users\chris\Work\ONAMA\onama-mobile-app\OnaMobile\OnaMobile\obj\Debugetstandard2.0\Views\PdfViewPage.xaml.g.cs:22
  at OnaMobile.Views.PdfViewPage..ctor () [0x00008] in C:\Users\chris\Work\ONAMA\onama-mobile-app\OnaMobile\OnaMobile\Views\PdfViewPage.xaml.cs:19
  at OnaMobile.ViewModels.ResourcesPageViewModel.OpenResourceAsync (OnaMobile.OnlineResources.ResourceLink resource) [0x001ac] in C:\Users\chris\Work\ONAMA\onama-mobile-app\OnaMobile\OnaMobile\ViewModels\ResourcesPageViewModel.cs:186

iOS SDK 14.1, ARM64. Happens regardless of Linker Behavior setting.

The page itself has nothing in its code-behind other than the default constructor calling InitializeComponent(). In the XAML, the RadPdfViewer control is in a two-row, one-column grid, where it is in the second row:

<Grid VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand" ColumnSpacing="0" RowSpacing="0">
    <Grid.RowDefinitions>
        <RowDefinition Height="60" />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>

    <Frame Grid.Row="0"><!-- ... --></Frame>

    <pdf:RadPdfViewer Grid.Row="1" HorizontalOptions="Fill" VerticalOptions="FillAndExpand" Source="{Binding Source}" />
</Grid>