Windows 10 uses File Associations to determine which program will automatically open a specific file type on your computer. For example, Microsoft Edge will opens .PDF files by default. 

​There are Two Methods to change the File Associations in Windows 10. 

Method 1: 

1. To change the file association for a specific file type, Right-click a file and Select Open With > Choose another app. 

2. Select a default program for the selected file type. Once you have selected a program, Check the box next to "Always use this app to open .pdf files" and click OK. 

Method 2: 

Use the Settings to view and modify the full list of file associations available in Windows 10. 

1. Open the Settings App and select System 

​2. In Default apps, select Choose default apps by the file type

​3  The default program is listed on the right of each file type. To modify the default program for PDF files, Scroll Down to PDF file type and click the icon of current default program. Select the program you want to set as Default Program