Sometimes a "file association" error occurs on your computer, which prevents Adobe Digital Editions (ADE) from opening downloaded eBooks. If you're having trouble opening eBooks in ADE, try the steps below to make sure that your computer (Windows or Mac) opens ACSM files (which are used to download eBooks) in Adobe Digital Editions.

Additionally, if you're using the Firefox browser, you'll also need to change the ACSM file association there (to make sure Firefox opens ACSM files with the correct program).

On Windows Vista, 7, 8, or 10

1. Windows 7 or Vista: Click Start, and type "Default Programs" into the search box and press Enter.
   Windows 8: Use the Search charm to search for "Default Programs."
   Windows 10: In the search bar at the bottom of the screen, type "Default programs" and select the result.
2. Click Associate a file type or protocol with a program.
3.   Scroll down, and select the ACSM file type.
   
4.   The extension should be set to "Adobe Digital Editions [version number]" (under "Current Default"). If this is not the case, click Change program . . .
5. Windows 7 and Vista: Select Adobe Digital Editions from the "Recommended Programs" list, or click the Browse button and select DigitalEditions from one of the locations listed at the end of this step.
   Windows 8: Select Adobe Digital Editions from the list, or select More options, scroll to the bottom of the pop-up window, and select Look for another app on this PC. Then, select DigitalEditions from one of the locations listed at the end of this step.
   Windows 10: Select Adobe Digital Editions from the list, or select More apps, scroll to the bottom of the pop-up window, and select Look for another app on this PC. Then select DigitalEditions from one of the locations below. 
   Locations:
   • 64-bit systems: C:\Program Files (x86)\Adobe\Adobe Digital Editions
   • 32-bit systems: C:\Program Files\Adobe\Adobe Digital Editions
   Note: You can find your system type by searching for System on your computer. Select the option under "Control Panel."
6. Click the OK button to save the changes. 

On Mac

1. Find the ACSM file on your computer (by default, it will go in your Downloads folder), and control-click on it. 
2. Click Get Info. 
   A file information window opens. 
   
3. Expand the Opens with section. 
   
4. Click the drop-down menu, and select Adobe Digital Editions. 
5. Click Continue and close the info window.