Our firm uses third-party software that is integrated with Adobe Acrobat. Acrobat DC was just pushed out this week and something we've noticed is that if we had any buttons from the third-party software added to the Quick Tools Toolbar, when you first open a document they are not displayed. The quickest workaround we've found to get them to display is to click on "Tools" and then "Document" again, and the buttons will then display in the Quick Tools Toolbar.
I googled a bit and saw other people were experiencing the same issue:
I contacted the maker of the software and they said they have no control over how buttons are displayed in the Toolbar, and that is something that Adobe would need to fix.
Operating System: Windows 7
Acrobat Version: Standard DC
Version Number: 2015.006.30198 and 2015.006.30243
Release: 2015 Release (Classic)
Thanks in advance!