The error on Windows 7 usually appears when launching a game or application that requires DirectX 11 or newer graphics features. This DLL is part of the DirectComposition API, which was introduced in Windows 8, but some newer software attempts to use it on Windows 7, causing this error.

Downloading individual DLL files from "DLL download sites" is risky:

Sometimes, applications confuse missing dependency files. While dcomp.dll is a DirectX file, ensuring your C++ runtimes are up to date is good practice to prevent crashes.