Please note that the error message could vary. Some of the common cases are: missing, corrupted, crashed, not found etc.
d3dx9_40.dll is a DLL file part of Direct3D 9 Extensions program which is developed by Microsoft. In order for the program to work properly, it needs a properly working dll file.
If you have visited this page and looking for the d3dx9_40.dll file, you have mostl likely encountered one of the following errors below:
In order to fix the d3dx9_40.dll error, you will need to download and install the DLL file in the appropriate directory. First, look at the download section on this page and get the corresponding version to your operating system. Pay close attention to the architecture of the file (either 32 or 64 bit), but also look for the language version. If there are multiple versions available we recommend you go with the latest one available.
Once you have downloaded the d3dx9_40.dll file, make sure you extract it using WinRar or a similar tool and place it in the directory where the faulty program is located. If this doesn't solve your problem, you may also want to copy the downloaded d3dx9_40.dll file in your System32 folder for 32Bit systems or SysWoW64 folder for 64bit based OS.