How to make any PDF document (at least the ones that aren't encrypted) fill able:
1. Get a copy of Adobe Acrobat Professional (This guide is made with 7 or CS2)
2. Design a form in any program you wish. Once the form is done, print it to the Adobe Acrobat Printer, and save.
........now we begin adding fields
3. Open the PDF in Acrobat, if not already open.
4. Turn on the Advanced Editing Tool Bar. (View > Toolbars > Advanced Editing) From this toolbar you can do some pretty nifty stuff. We will be concentrating on the Forms Tools. By default, the Button Tool is shown first in the Dropdown box. At the bottom of the Dropdown, it gives you the option of viewing the Forms Tools Tool Bar...DO IT!!!
We will be using the Text Field Tool, and the Check Box Tool.
5. Add the text fields to the PDF. Make sure that when doing so, you add all of the text fields in the general area and set them to the same height. Then proceed to align them.
a. Add the fields
b. Make all the fields the same size by selecting all of them using the pointer tool 
> right-clicking > size > height.
c. Align them to the base line (or if in blocks, size them to fill the interior of the blocks and skip 6). Be sure to zoom in ALL THE WAY to get them dead on...you may ask why I would do this. Well, I do it because then it looks perfect...got a problem with it, then close your browser.
...Also, make sure that the bottom of the text box sits right on top of the base line...not over it. Expand/Decrease the width of the text boxes on the other side to align them to the base line.
d. Should look like this when all aligned.
6. Now that the fields are in place, we need to add text to them to test the text size. Normally, you will want the text to be small at this point (especially if you are adding fields to base lines and not text boxes). So once you have text in the fields, select all of the fields and use the ctrl + UP/Down respectively to make the fields taller/shorter. You will notice that as you do this, the text is not properly aligned on the base lines...this is okay. Once you have the text to an appropriate size, simply use your Up/Down keys to position the text on the base lines.
a. Add the text.
b. Now select all of the text boxes, and use the ctrl + Down key to increase the size of the boxes (MAKE SURE ALL BOXES ARE SELECTED WHEN DOING THIS).
c. Use the UP/Down keys to position the baseline of the text within the text boxes to align with the base line of the existing text. (MAKE SURE ALL TEXT BOXES ARE SELECTED WHEN DOING THIS).
Why do we do this you may ask? We do it because it is aesthetically pleasing to the eye, and only takes a miniscule amount of effort to do.
..........So you ask, what is the baseline of text? "The baseline is an imaginary line on which the text sits. Characters like lower-case 'j' and 'q' have decenders which extend below this line."
Presto....you have a fill able form. I will go into Check Boxes and Tab Order when I get a chance.
Now I'm going to go into tab order.
For those of you who have never heard of tab order (you know who you are) it is the order in which focus (another term you might not of heard used before when it comes to documents or programming) is given to objects down the document as the user hits tab.
Why do we care to set the tab order, isn't the user just going to use their mouse to advance to the next field? Normally, NO! On the very rare occasion you get a NEWB that doesn't know how to type that will end up using their mouse no matter how many times you hit them in the head with it. However, normally everyone else will type, and mindlessly hit tab to advance to the next object. Which is why we set the tab order, otherwise the user might get lost on the document...and if that isn't frustrating, getting struck by lightning is.
So to set the tab order for your objects, you must first select them all. (by the way, if you created all of your objects in order, then you don't have to do this as Adobe has already given the objects the proper tab order)
Once they are all selected, right click on one of the objects, and click on "Set Tab Order".
Now you are viewing the tab order of the objects (small number in the top left). If the objects are already in order, then you are done. If not, then we need to fix them, and they probably look similar to this:
To fix this problem, simply click on the objects in the order in which you would like the user to use them. If you screw up, start over. Once you are done, they should look similar to this (numbers in the correct order).
Now that the objects are in proper working tab order, you need to exit the tab order mode by simply RIGHT-CLICKING on any one of the objects and clicking on "Set Tab Order".
This concludes tab order. If you have any other questions, google will be happy to answer them for you (or send you in the wrong direction).
