The answer depends entirely on where you downloaded it.
The most reliable way to fix this is to download the directly from Microsoft’s official website . d3x9-26.dll
"D3dx9_26.dll is either not designed to run on Windows or it contains an error." How to Fix d3dx9_26.dll Errors To resolve these issues, follow these steps in order: 1. Install the DirectX End-User Runtimes The answer depends entirely on where you downloaded it
Technical Analysis: The Architecture and Legacy of d3dx9_26.dll d3dx9_26.dll is a core component of the Microsoft DirectX 9 d3x9-26.dll