The values in the forms are not displayed in the document visualized from the viewer. 

For some TrueType fonts, the spaces are displayed as rectangles.

Some Image XObjects are imported but not displayed in PdfViewer.

Some Image XObjects are imported but not displayed in PdfViewer.  This behavior usually occurs when the document contains scanned images.

Text in specific pdf files is not visible in the viewer.

The text is not visualized due to the negative value for font size. 

Paths in the documents are not visualized in the PdfViewer. 

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.

 

An implementation of JPXDecoder should be created to allow the decompression of data encoded using the wavelet-based JPEG2000 standard.

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.

Some Shading elements are not property imported which leads to unexpected drawings on the exported (previewed in the PdfViewer) document.

System.ArgumentException: Unsupported touch action type.
Parameter name: actionType
   at Telerik.XamarinForms.SkiaSharp.Interaction.SkiaViewInteractionAdapter.Convert(SKTouchAction actionType)
   at Telerik.XamarinForms.SkiaSharp.Interaction.SkiaViewInteractionAdapter.OnTouch(SKTouchEventArgs e)
   at Telerik.XamarinForms.SkiaSharp.Interaction.SkiaViewInteractionAdapter.GlView_Touch(Object sender, SKTouchEventArgs e)
   at SkiaSharp.Views.Forms.SKGLView.OnTouch(SKTouchEventArgs e)

is thrown when scrolling the document using the mouse wheel and using latest official SkiaSharp Views Forms version 2.80.3

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.

Provide support for lots of image formats when exporting PDF documents.

The glyphs are rendered with additional unexpected lines when a specific custom Type 1 font is used to show them.

For example page loaded event: the purpose of the event to get a callback whenever a page is loaded and the page information is available.

Support for horizontal scrolling the Pdf document in the viewer: 
Horizontal single page (go through the pages swiping/scrolling left and right)
Horizontal multi-page stacked (not possible, go through the pages swiping/scrolling left and right)

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.

Currently, importing a document with non-embedded TrueType font will result in a font instance with an empty font source. Support should be added for providing custom font data of TrueType fonts during document import.

Pdf document is not loaded when it contains Type1Font "middot" glyph.