Security notification when opening PDF files in powerpoint

Hello,
We're having an issue on Dell Latitude 10 tablet which seems to be hard to resolve.
I've configured Windows reader as default program for all PDF files.
When opening PDF files in a Powerpoint presentation the following Microsoft Office notification pops up:

Opening XXX
Some files can contain viruses or otherwise be harmful to your computer.
It is important to be certain that this file is from a thrustworthy source.
Would you like to open this file?
OK/CANCEL

When clicking OK, the file opens. It is asked every time when opening a PDF link in the presentation.
Same issue when you configure Adobe reader touch as default.
When setting Adobe Reader XI as default, you don't get the message. But then, we don't want the files to open in that last one.

We've been searching to resolve this in the powerpoint options e.g., but without success.

Thanks to everyone who can give us a lead.

That is correct, that you will get that message. It was implemented, due to Adobe still not resolving issues with Acrobat. Microsoft issued this security update some time ago for Office 2k7, 2k10, 2k13.

Oh, so i guess there is no workaround to avoid that message?
That's a pity.
We'll have to think about doing it differently then, because it's not very handy when giving a presentation in front of your customers
Thanks!