I have several computers in the office and this is the only computer with this problem. When I go to irs.gov/formspubs/index.html and then search for form 7004. I find the form and open it but I can't enter any text in the fields. I am using Adobe Reader 9 and everyone else has an older version.
The IRS uses a server side product to create fillable and saveable forms. The product is outdated so they won't work with anything over Reader version 8.
My company works with the IRS. I know they were making an effort to make more of the forms fillable for this year, but I don't think the 7004 is one of them. In fact, you probably noticed the form hasn't been updated for 2009. The 2008 form is the one to use for TY 2009.
One alternative is to e-file the 7004 right to the IRS. That way you get an ackowledgment from the IRS that they have A) received your request and B) accepted or rejected it. If you mail in a 7004, you won't get either.