Adobe PDF pop-up

To remove, navigate to Add-ins in Outlook Options:

File tab > Options > Add-ins

From there Outlook Options will appear. At the bottom you will manage COM Add-ins and click Go...

 The COM Add-ins dialog box will appear:

Uncheck the Add-in(s). Its either Acrobat PDFMaker Office COM Addin After you have unchecked the Add-in(s), click OK. Outlook will close and restart. If it doesn't, close Outlook and reopen it. The PDF message should no longer be there.