I would not expect any other behavior. The Picture attribute is only designed to display common image file types. You can consider using a server-side utility to extract an image from a pdf file. I came across this but did not study it or use it, but its pdfimages command seems appropriate for this task.
https://github.com/elswork/poppler-utils
I use PDFtk (PDF Toolkit) to merge pdf files on the server side so something like this may work. I imagine complications if the document has more than one page or image embedded.
p.s., I checked with Grok on how the Kendo picture widget works. Answer follows:
No, the Kendo UI photo/picture widget—typically referring to the ImageEditor component—cannot display PDF files. It is designed for raster image editing and supports only common image formats such as JPEG, PNG, BMP, and non-animated GIF. PDFs are not among the supported formats, as they require specialized rendering for multi-page documents and vector content.
For displaying PDFs in Kendo UI, use the dedicated PDFViewer widget instead, which renders PDF files directly in the browser with features like toolbar controls, scrolling, zooming, and page navigation.
