D3dx9_28.dll is one of many Microsoft's Direct-X DLL (dynamic link library) files. If you see DLL file beginning with d3dx9 on your computer, it will relate in some way to Microsoft Direct-X. Direct-X is used for games and CAD programs primarily, and Direct-X is commonly responsible for displaying graphics, 3D videos and animation.
D3dx9_28.dll along with other DLL files with similar names is used with Microsoft's Direct-X application. The d3dx9_28.dll file is usually installed when you either install Direct-X from Microsoft's website, or when a software application that uses Direct-X is installed. These DLL files are used to correctly display animations and complex graphics, and also are responsible for reproducing audio and surround sound. Direct-X was developed primarily to display graphics and produce sound on gaming systems and consoles including Microsoft's Xbox and Xbox 360. It has since been adapted to run on PC's and cater for PC games and software.
D3dx9_28.dll errors usually indicate a damaged, missing, or corrupt DLL file. If this is the case, you may see one of the following:
D3dx9_28.dll will appear mostly when a program or displaying 3D graphics is run. Games that use Direct-X for 3D animations will tend to crash when you run them, other applications or software may display messages at start up. In worst case scenarios, your computer may freeze or crash.
Nearly all error messages mentioning d3dx9_28.dll will be somehow related to Microsoft Direct-X. You may also receive messages relating to d3dx9_25.dll, d3dx9_32.dll, and d3dx9_28.dll. All of these files are connected to Direct-X, and the solutions to repair or replace these files are very similar.