Custom document properties overview
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
When you build a document-level project, Visual Studio adds two custom properties to the document in the project: _AssemblyLocation and _AssemblyName. When a user opens a document, the Microsoft Office application checks for these custom document properties. If they exist in the document, the application loads the Visual Studio Tools for Office runtime, which starts the customization. For more information, see Architecture of Office solutions in Visual Studio.
Applies to: The information in this topic applies to document-level projects for Excel and Word. For more information, see Features available by Office application and project type.
_AssemblyName
This property contains the CLSID of an interface in the Office solution loader component of the Visual Studio Tools for Office runtime. The CLSID value is 4E3C66D5-58D4-491E-A7D4-64AF99AF6E8B. You should never change this value.
_AssemblyLocation
This property contains a string that provides details about the deployment manifest for the customization. For more information about manifests, see Application and deployment manifests in Office solutions.
The _AssemblyLocation property value can have different formats, depending on how the solution is deployed:
If the solution is published to be installed from a Web site, UNC path, or a CD or USB drive, the _AssemblyLocation property has the format DeploymentManifestPath|SolutionID. The following string is an example:
file://deployserver/MyShare/ExcelWorkbook1.vsto|74744e4b-e4d6-41eb-84f7-ad20346fe2d9
If you are running or debugging the solution from Visual Studio, the _AssemblyLocation property has the format DeploymentManifestName|SolutionID|vstolocal. The following string is an example:
ExcelWorkbook1.vsto|74744e4b-e4d6-41eb-84f7-ad20346fe2d9|vstolocal
The SolutionID is a GUID that the Visual Studio Tools for Office runtime uses to identify the solution. The SolutionID is automatically generated when you build the project. The vstolocal term indicates to the Visual Studio Tools for Office runtime that the assembly should be loaded from the same folder as the document.