The files with .mst extension are used to transform the content of an MSI package. They are commonly used by system administrators to apply the custom settings to an existing MSI file. The MST files are used together with the original MSI package in their software distribution systems such as group policies. MST files are generally used in software development and testing for configuring their under development versions of the software.
MST file format
An MST or Transform file is used to collect the installation options for programs that use the Microsoft Windows Installer in a file. These files are commonly used on the Installer (MSIEXEC.EXE) command line, or used in a Group Policy of software installation; in a Microsoft Active Directory domain. The MST files can also be used with wrapped executable installers. A general case is that someone wants to pass command line parameters to the wrapped installer. In order to do that you need an MST file that adds the WRAPPED_ARGUMENTS property to the property table. These files can’t be create or edit using general editors. Specific tools are available for this purpose.
How to use MST files?
The MST files can be generated by using various tools and Ocra is generally used to generate an MST files. Then settings can be customize according to the need and save them at a specific location. After that the MST files can be used in in conjunction with MSI files. If you want to test this files; use the following syntax on the command line
msiexec /i setup_1.0.msi TRANSFORMS=mylog.mst
You can also use TRANSFORMS property of Windows installer which is actually a list of the transforms that the installer applies when installing the package. The installer executes the transforms in the same order as they are listed in the TRANSFORM property. Transforms can be specified by filename with .mst extension or full path. To specify more than one transforms, separate each file name or a semicolon like following example.