When Microsoft introduced Windows 10, they removed the ability for enterprise administrators to mandate which applications users had set as their defaults - instead giving the users the power and ability to choose and set their own as they preferred. This also means that Windows built-in and Store applications (such as Edge, Mail, Photos etc) are automatically set as the default when a user first logs in, and cannot be changed by any enterprise management systems - only by the user them self.  This is not ideal in some situations (e.g. when unconfigured applications such as Mail choose to try and open mailto: links, or when Edge assumes control of all PDF extensions).

Users can very easily resolve this issue for themselves, by choosing which installed applications they would like to use as the default:

• Open the "Settings" applications (either from the Start Menu - the small cog above the "power" icon, by typing "Settings" into the Windows Search bar, or by choosing "All Settings" from the action centre:

• Choose "Apps (Uninstall, defaults, optional features)" followed by "Default Apps":

• Finally, click on the function you'd like to change the default application for (e.g. Email, Web browser" etc) and choose from the options available (Windows will only show you applications which are installed and report the ability to handle the function you've chosen):

• To change the default programs for additional file types, click on "Choose default apps by file type" at the bottom of the window:

• Then scroll down the list to find the file type you wish to change (eg .PDF).  Then click on the program next to it and select the program you wish to use instead: