Acrobat Pro XI - I can't seem to be able to edit font sizes in a PDF Fillable Form

Question

I have a PDF fillable Form which I wish to complete except for a few fields that need to be completed each time the form is submitted, and save it with those static fields completed and signed with an image of my signature.
Sometimes the font seems to auto change it's size to fit in the field it is intended for, other times it is either too small to read or too large to fit in the box and be readable.  I've chosen the arrow tool and the menu choice Edit; Edit Text and Images, and they don't really seem to do anything.
One part of the form has two fields for phone numbers (Business and Home) and the Business entry is always too tiny to read, while the Home field is OK. 
Aside from that, there are also two boxes with drop down menus which say Select with an arrow next to them, and one of them for example has choices of Male and Female.  If I select one, later when the form is printed, the gender choice is overprinting on the word Select, making it hard to read.

Answer 1

Thanks for explaining that.  I wish I had "Locked" all the fields before I started then, since I did get somehow get a couple of them rearranged by accident and it took some (not a lot) of work to get them back in the proper order.
For the present file, which I am not adding captions to, how would I set the "read only' property?  I looked around in the Tools area and the only thing that looked possible that I found was Protection; Restrict Editing but I didn't go farther yet because it wanted me to set a password before proceeding.
Is it possible to make individual fields "Read Only" rather than the whole document?
As for the signatures, what I did is sign on a piece of paper, scan that into a JPG file, and then choose "Sign" from the top menu bar between the Tools and Comment choices:
This allowed me to drag the image of my signature to the line on the form where I am supposed to sign it, and place it there.  Then when I save the form with that signature on it, if I open it again and go to Forms Edit, I get a message that the form contains no Form Fields, and asks it I want Acrobat to detect fields for me.  If I choose yes, it then detects fields that were not previously filled in, but not the fields in which I had placed default entries before saving it.
I see where you mean about Signature on the left pane, but if I open that after loading a PDF that I signed using the above procedure, it detects no signature.  So the "Digital Signature" you mention must not be the image of the signature like I am using.  So if I want to  make the image of my signature into a "Digital Signature" that can be verified, do I have to go to some third party paid procedure like Verisign or EchoSign or something or can I somehow self certify the image of my signature?
I notice, as a side issue, that if I upload the blank unmodified PDF Form to Acrobat.com, it lets me fill it out and saves the file with a "form" extension, and they have a menu choice to Sign, but if you choose that you just get a box in which it expects you to draw your signature with your finger or a stylus I guess, but the result doesn't look much like my signature, and then if you save it to the computer, it does save it as a PDF file, but if you try to print it, the printed document is blank, so that is kind of useless.
Thanks for your continued help!