From initial versions of Adobe Reader, its search box behaves (in Windows) a different way than any other dialog box.
When I try to select part of the searched text to change it, it lets me select it, and only when I release the mouse button, it selects everything.
It is not possible to accustom it, because the whole Windows environment behaves different way.
So it makes me angry every day for decades!
I suppose there is not any settings or workaround for this problem, so this behavior should be changed.
BTW, I do not understand why this was made this way?
For instance, the Foxit reader uses a search box which behaves normally.