How to create .docx files and .xlsx files on Android

Question

I have a very simple question: How to create .docx and .xlsx files on Android. Before someone marks this as duplicate, let me tell you that

Answer 1

Use Apache POI library only because It is the best out there.

Google also uses it in its Quick Office Application for Android.

For the .***x files like docx and xlsx, It might have some limits on the allowed functions in Dalvik.