Windows has many programs available that can handle your files. You can have several apps that can open a single type of file, like PDFs or text documents, and really only prefer one of them. There are ways to select your default program for different tasks.

Windows 7

In Windows 7, there's one place to change your default program settings.

1. In the Start Menu, select Default Programs.
   
2. Select Set your default programs at the top of the page.
3. Find the program you want to use for defaults in the list on the left and click it.
4. In the main section of the window, you'll have two options:
   1. Set this program as default, which will take any file types the program lists as things it can open and sets it so they open in that program
   2. Choose defaults for this program, which opens a list of all the different file types the program is capable of opening. You can then select any or all of the file types you want to use with this program and press Save.
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         1. Select OK to finish.

Windows 10

In Windows 10, the default app options are located in the Settings app.

1. In the Start Menu, select Settings
2. Select System
3. Select Default Apps in the left sidebar

There are a few options you can change on this page, the most likely being Web Browser. If you want to change something not listed on this page, select Set defaults by app at the bottom of the page. This is the same menu as in Windows 7, so see step 3 of the Windows 7 section above.

Changing the Default Program for a file type

In order to change what program a file type opens with: 

1. right click on the file that you would like to open.
2. Click on Properties at the bottom of the menu.
3. Next "Opens with: ... ", Click on "Change."
4. Click on the program you want to set as default. (For PDFs you will want Adobe Reader)
5. Click OK. You should now be able to open that file from the program you set it to.

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