Would you please describe your problem in more details?
Does your iPhone 6+ use Wi-Fi or Cellular Data to download apps from the App Store? Can you download any other apps?
Please launch the App Store app on your iPhone 6+ and search for "Adobe Acrobat".
Which icon do you see for Adobe Acrobat Reader?
(a) GET icon
(b) OPEN icon
(c) Cloud icon with down-arrow
What happens when you try to download the app? Do you see an error message?
If app installation gets stuck, please take a look at the FAQ document to see if it helps.
Please let us know what you find.
TY for your answer, but it seems OK now. I stopped my IPhone and I put it on again. All applications download.