Hi Andrei,
If the reference is compiled you need to use Reflection. If it is a project
reference, the VSLangProj.Reference class has a Project (or similar)
property to retrieve the project. From my web site
http://www.mztools.com/resources_addin_developers.htm, see the articles:
HOWTO: Navigate the files of a solution from a Visual Studio .NET macro or
add-in.
By Carlos J. Quintero, MZ-Tools articles
HOWTO: Getting information specific to VB.NET and C# projects from an add-in
or macro.
By Carlos J. Quintero, MZ-Tools articles
HOWTO: Navigate the code elements of a file from a Visual Studio .NET macro
or add-in.
By Carlos J. Quintero, MZ-Tools articles

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Best regards,
Carlos J. Quintero
MZ-Tools: Productivity add-ins for Visual Studio
You can code, design and document much faster:
http://www.mztools.com
>I made a custom VS project for the laguage; and I need to get symbolic
> informaton from C#/VB/etc projects, so intellisense in my project will be
> able to complete type names from referenced projects. How can I get this
> information?