If you have the latest Telerik.Reporting NuGet package (18.3.24.1112) installed simultaneously with the Telerik.Documents.Fixed NuGet package, indeed, the compile time error occurs:

The type 'Size' exists in both 'Telerik.Documents.Core, Version=2024.4.1106.20, Culture=neutral, PublicKeyToken=5803cfa389c90ce7' and 'Telerik.Reporting, Version=18.3.24.1112, Culture=neutral, PublicKeyToken=a9d7983dfcc261be'

This undesired behavior is not reproducible with the previous version of Telerik Reporting. This is caused due to the fact that Telerik.Documents.Primitives.Size is contained in both assemblies/packages.

Workaround: Resolving Compile Time Error with Telerik.Documents.Fixed and Telerik.Reporting after Upgrading to Q4 2024