If you use a single Grid in the Window it will be measured with the window size and the PdfViewer in row with height="*" should be measured in the same finite window height. In the other case when the mensioned Grid is inside some other element (for example Grid with row height="auto") then the inner grid may be measured with height Infinity and in this scenario PdfViewer will be measured with Infinity as well. This is the possible cause of the mensioned issue.
Could you please check whether in your scenario the Grid is nested in some other element measuring it in Infinity (Grid with row height "Auto", StackPanel, or some other content control)?
I am looking forward to contacting you again.
the Telerik team
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