To change the default PDF viewer used by BUSY, follow these steps:Step 1: Right-click on the PDF file you want to change the default app for.
Step 2: From the context menu, click on Properties.
Step 3: In the Properties window, look for the "Opens with:" section. Click the Change button next to it.
Step 4: A new window will appear, presenting a list of available applications.
Step 5: then you have selected Adobe Acrobat Reader, click "OK"
step 6: Back in the Properties window, click "Apply" and then "OK" to save your changes.