PrivateFontCollection is not working
The PrivateFontCollection is required for PDF and other renderings that need to measure text and prepare glyphs with the customers custom (not installed font) for layout purposes.
The PrivateFontCollection internally uses the GDI API calls like NtGdiAddFontResourceW that is blocked by the AppServices backend. This is confirmed by Azure representative.
Without the PrivateFontCollection in Azure AppServices only installed fonts can be used for rendering with Telerik Reporting and I suppose with many other similar products.