Missing Apps in the Open In Menu
If you have many apps installed on your iPhone or iPad that can handle the same file types, e.g. PDFs, it can happen that one or the other does not longer appear in the Open In menu that allows you to send files from one app to another. In iOS 5 the limit seems to be ten apps. So if you want to send a file to, e.g., DEVONthink To Go and you don't see it listed it may be that you simply have too many apps on your device that can open this file type.
So what's the solution? Remove one or two apps you use less often to free up space in the menu. Unfortunately it seems there is, yet, no way to persuade iOS to show more apps in Open In…
Read even more about this phenomenon on iPhone J.D popup: true.