It appears Acrobat Reader doesn't always allow copy/paste functions to annotate pdf files. Sometimes it does and other times not. Why? I am using latest Adobe Reader from Google Play Store on a Samsung Galaxy S7 with latest Marshmallow OS update.
We have tried to reproduce the same at our end and it worked fine.
Could you please share the work flow that you follow? from where exactly you are copying/pasting the text?
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