Usually, when someone creates a form as a PDF that they want you to fill in on a computer, they put fields in it that you can type into. Unfortunately not everyone who creates a PDF form knows what they're doing, so there may not be any such fields. (Here
I'm thinking of a particular giant insurance company that must remain nameless...)
There are a couple of ways to add text with Word. Which one is best depends on whether you need to print the final version and mail the paper, or whether you need to submit it electronically. It also depends on whether the form is one page or more than one
(if you insert a multi-page PDF into Word, it will only show the first page).
For a print-only final version of a one-page form: Click Insert > Object. In the dialog, click the From File tab, click Browse, and locate the PDF file. Click Insert. This puts a (non-editable) picture of the form into the Word document. If necessary, you
can grab its corners and resize it to fit the page. Before you do anything else, press Ctrl+Home to make sure the picture is not selected. Then click Insert > Text Box and choose Draw Text Box from the bottom of the menu. Draw a text box on top of the picture
in one of the places where text is needed, and type into it, then save. Repeat the draw-type-save sequence until you've completed the form. Then print it.
For electronically submitted and/or multi-page forms: Click this link: http://www.google.com/search?q=pdf+to+word+online+free+converter. Use any one of the first half-dozen results to convert the PDF to a Word document. Some of the sites may reproduce the original form's fonts and layout better than others, but I can't tell
which ones. Treat the result like any other document. If the school needs a PDF file instead of a Word file, use Word's command File > Save & Send > Create PDF/XPS Document.