To set Windows to open a specific type of file automatically, you can use the File Types tab in the Folder Options dialog box. To do this:
1. Open the Control Panel.
2. Select Appearance and Personalization.
3. Click on Folder Options.
4. Go to the View tab and uncheck the box next to Hide Extensions For Known File Types. This will allow you to view the file extensions.
5. Go to the File Types tab. This is where you can manage file associations.
6. In the Registered File Types list, find the type of file you want to open automatically. If it is not already listed, click New and add the appropriate file extension (e.g., .pdf).
7. Select the new file type from the list and click Advanced.
8. In the Actions list, select Open, and then click Edit.
9. In the Edit File Type dialog box, enter the command for opening the file type. Typically, this is the path to the executable for the relevant program (e.g., C:\Program Files\Adobe Acrobat Reader\AcroRd32.exe). Make sure to include any additional parameters if necessary.
10. Click OK to close the dialog boxes.
11. Close the Folder Options dialog box.
From now on, whenever you double-click a file with that extension, the associated program will be launched automatically.