For the life of me I cannot edit the smaller text box area that is totally contained by a larger one. I just need to edit the text on this smaller box but unsure how I can access to it. I can select the text with the arrow but the edit cursor will not select the smaller box contained in the larger box, just opening up editing on the larger one every time.
Using Adobe Acrobat Pro DC:
click outside the bigger textbox to unselect it
Zoom in extremely deeply.
try clicking so, that your cursor will be entirely inside a (black) letterform of your smaller text box
I tried this a few times - and you need some luck and patience, but it can be done. The selection-markers for the text-frame will tell you when you got it right.
In Corel it used to be: Hold the ALT key and click the area several times until the lower object which you want is marked as selected. If there is something similar in Adobe, I have not found it.
Here is another working method, if you are couragious:
Select the bigger box and hit CTRL-X to cut it out. It will stay in your clip-board. Now easily edit the lower smaller text (but do not use any tool which would involve your clip-board of course (unless you have a clipboard manager like AceText)).
Once you are done editing, click outside the smaller text to unselect it. Then just hit CTRL-V to paste; and the bigger text will be put back to its original location.
Both not great solutions, but I guess that you will not do real heavy editing in an existing PDF document; probably just tweaking some typos or such, eh?