What is a .dll file?

About the format

A .dll is shared program code: a PE binary like an .exe, but designed to be loaded into other processes rather than run on its own. Windows itself is thousands of DLLs; every application loads dozens. Common DLL situations: an app refusing to start with 'VCRUNTIME140.dll was not found' (install the Microsoft Visual C++ Redistributable — never download the single DLL from a random site); a crash report blaming a specific DLL (that module — often a plugin, overlay or driver component — took the program down); or an unknown DLL appearing in a scanner report (check its digital signature and location). Copying a lone DLL into System32 to 'fix' an error is the classic wrong move: missing-DLL errors are almost always missing runtime packages, and 'DLL download' sites are a well-known malware channel. Double-clicking a DLL does nothing by design, though DLLs can host code invoked via rundll32 or by being planted where a program will load them.

How to open a .dll file

Is a .dll file dangerous?

DLLs are executable code. One from an untrusted source can be as harmful as an .exe — it just needs a host process. Never source DLLs from 'DLL download' sites.

Related file types