Type Libraries describe most COM objects, including both Automation objects and ActiveX controls. A Type Library can exist in one of the following forms:
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A separate file with the extension
.tlb or
.olb. This file is usually in the same directory as the main binary file for the Automation Server or ActiveX control.
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Part of the main binary file for the Automation Server or ActiveX control, generally with the extension
.exe,
.dll, or
.ocx. This is often the form provided with ActiveX controls.