Answer
Change the Default by Using Open With in File Explorer
Change the Default by Using Default Programs in Control Panel
Change the default by modifying the Registry
Change the Default by Using Open With in File Explorer
1. In your File Explorer, right click on a PDF file, select "Open With", select "choose another app" to open the box "Select an app to open this .pdf file".
2. Select Foxit PDF Editor or Foxit PDF Reader from the list, and check the option "Always" to apply the change.
If Foxit app is not listed in this box, you can scroll down to see "More apps" link. Click this link to browse Foxit app. If still not see Foxit, scroll down to see "Choose an app on your PC" link. Click this link to browse to Foxit and choose the "Open" button to set it as the default.
Change the Default by Using Default Programs in Control Panel
Open Control Panel and select "Default Programs" to bring up the "Apps > Default Apps" panel. Please input ".pdf" into the "Set a default for a file type or link type" field. Below this field, the current default program for the .pdf file format will be displayed. Next, click the "Change Program" button located on the far right of the currently displayed default program.
A pop-up "Set a default app for .pdf files" dialog box will appear that will let you choose an app from the list. Please select Foxit PDF Editor or Foxit PDF Reader from the list, and check the option "Always" to apply the change.
If Foxit app is not listed in this box, you can scroll down to see "More apps" link. Click this link to browse Foxit app. If still not see Foxit, scroll down to see "Choose an app on your PC" link. Click this link to browse to Foxit and choose the "Open" button to set it as the default.
Change the default by modifying the Registry
1：Press the Windows key + R to open the Run dialog box. Type in "regedit" and press Enter. This will open the Registry Editor. Navigate to the “HKEY_CLASSES_ROOT\MSEdgePDF” key. You can do this by expanding the folders in the left-hand pane. Right-click on the MSEdgePDF key and select Delete. Confirm the deletion and close the Registry Editor.
2：Then, open Foxit PDF Editor or Foxit PDF Reader again, click on Help > Set to Default PDF Reader to bring up the "Apps > Default Apps" panel. Next, follow the method provided in the section above, Change the Default by Using Default Programs in Control Panel, to set Foxit PDF Editor or Foxit PDF Reader as the default program.