Like IOS App iBook there is a feature , if u don't the meaning of any word u can just hold that word for 2-3 sec, u will automatically get the meaning of that word but I didn't found this feature into adobe acrobat reader and I don't think so that this feature take so much work it simply done with add a dictionary.
So please have attention on this feature and let me know if there is any alternative of this.
[topic moved to Reader/Acrobat DC for Mobile forum]
Unfortunately, we don't support this feature right now. We have taken note of this feature request and would try to incorporate it in the application in future releases.
Acrobat DC Mobile Team