|To set the autoinstall option for an application|
Open Group Policy Software Installation.
In the console tree, click Software installation.
In the results pane, right-click the application that you want to be installed automatically when the user tries to open a file with the associated extension.
Click Properties, and then click the Deployment tab.
Under Deployment options, select the Auto-install this application by file extension activation check box, and then click OK. This option is recommended, and it is selected by default.
To complete this procedure, you must have Edit setting permission to edit a GPO. By default, members of the Domain Administrators security group, the Enterprise Administrators security group, or the Group Policy Creator Owners security group have Edit setting permission to edit a GPO.
The autoinstall option will only apply if there is not currently an application for the associated extension.