Go to Add-Ins - VSdocman menu or press VSdocman button on standard toolbar. VSdocman dialog appears, select Project Properties pane. Set Output - Platforms & Frameworks page.

Platforms shown in documentation
A text that will be shown in Platforms section on each member page. This is usually comma delimited list of supported platforms.
.NET Framework
Comma delimited list of supported .NET Framework versions. Leave empty if none. It will be shown on member pages in some output formats.
.NET Compact Framework
Comma delimited list of supported .NET Compact Framework versions. Leave empty if none. It will be shown on member pages in some output formats. Moreover, if this field is not empty, the "supported by CF" icon will be shown besides the member name in member list.
XNA Framework
Comma delimited list of supported XNA Framework versions. Leave empty if none. It will be shown on member pages in some output formats.