Hi,
I noticed that when I have a PDF file already open in Acrobat Pro DC, for instance opened it from a local disk, and then want to open a PDF attachment in Microsoft Outlook, it fails with the "Acrobat failed to connect to a DDE server." error message.
However, if I just close the PDF that is open and then try to open the PDF attachment of an email in Outlook it opens with no problem. Similarly, if I already have an PDF attachment open from Outlook (not a PDF instance from local disk, e.g.,) then when I try to open another PDF attachment in Outlook, it can open again with no problem.
The opposite case, fortunately, does not cause errors. I.e., if I first open a PDF attachment in Outlook and then try to open PDF files from local hard disk, it opens them successfully.
Btw, I noticed it is the same case when I open a PDF file from my browser while already having one from local hard disk open!
In short, it seems if I already have open PDF files from one source (e.g., hard disk), and then try to open a PDF attachment from another source such as Outlook or Firefox, it fails.
How is it possible to fix it? It is so frustrating that I have to close all my working PDF documents just to be able to view a PDF attachment.
Thanks.