You can find all of the installed apps in the following folder:
C:\Users\Public\Libraries\Apps.library-ms. The applications will be listed as APK.
Bluestacks uses the following folder as a shared folder:
C:\ProgramData\ BlueStacks\UserData\SharedFolder. In the interface, install a file manager and copy the APKs to /sdcard/bstfolder, then browse the Windows directory and you will see all the moved APKs.