Download php_mssql.dll file from DLL library collection and OCX elements. Perhaps this file will help you to correct the error "the php_mssql.dll library is not found" which appears as a result of incorrect operation of the Windows operating system or work with the program.
How to download free php_mssql.dll?
Also, this file may be required when developing software. If you use the php_mssql.dll file, you should review the copyrights to it.