The Group Policy is a Microsoft Windows feature that allows you, as an administrator, to create a set of rules and control the working environment of all users that have access to a specific computer. With Group Policy, you can change certain settings to restrict file association. File association is essentially a policy that triggers a specific application or software to run when you open a certain file extension. Note that you will require administrative rights and a server computer to perform this task.
Log in to a server computer that has administrative rights and privileges.
Click the "Start" menu and select "All Programs." Click the folder labelled "Administrative Tools."
Click to launch "Group Policy Management Console."
Locate the server object folder where you wish to enforce the policy. Right-click the folder and choose the option "Edit."
Click "Computer Configuration."
Click "Control Panel Settings."
Locate "Folder Options" and right-click it.
Choose "New" from the context menu. Select "File Type."
Click the "Actions" drop-down menu and choose the option that says "Create."
Click the "File Type Settings" drop-down menu and choose the option that says "File Extension."
Type the file extension (for e.g., .doc, .pdf, .mp3, .jpg) you wish to enforce and restrict.
Choose the program under "Association." Click "OK" to end task.