Try this:  http://www.archives.gov/exhibits/charters/constitution_transcript.html

They have an option to download a copy.

Mary Yonkers I downloaded a copy on my Kindle but see you have lots of help already.  The only thing that I might suggest is checking these links: 

http://www.dummies.com/how-to/content/us-constitution-for-dummies-cheat-sheet.html

https://www.mindflash.com/blog/2011/01/the-10-minute-guide-to-the-u-s-constitution/

http://www.usconstitution.net/constquick.html

I carry a copy around in my car.  But here's a pdf. 

Mary Yonkers Here are a couple of links:

http://www.usconstitution.net/const.pdf

https://www.gpo.gov/fdsys/pkg/GPO-CONAN-1992/pdf/GPO-CONAN-1992-7.pdf

TRY THESE:

http://www.usconstitution.net/const.pdf

http://constitution.findlaw.com/amendments.html

amendments

High school students studying the constitution? You might want to tread carefully on that one lest you be labeled as a terrorist by the Obamanites. 

http://www.usconstitution.net/const.pdf

I would assume that the National Archives in DC would have it.  After all, they have the original on display during viewing hours.

Tammy Lankford gave an excellent link.  So did many others.

And what Val Evans said... hopefully your high school students are aware of the threats to our Constitution from Obama, aided and abetted by the Republican Congress.

Hope it's a great event...  Have fun!

http://www.usconstitution.net/const.pdf

National archives or the library of congress.  I believe that is where I downloaded my copy last year on July 4th.

This may be the same link Patricia Kennedy found.

Oops, too late. I see you have been provided lots of good links.

Good luck, Mary.... I don't have an answer for you....

Mary, it looks like you have many links to choose from.  I am surprised that you were unable to find a down-loadable pdf.

What a wonderful experience ... and yes, judges will want to be as smart as the students

I don't have a link but I see that many supplied it anyway- good luck with the speech contest!!!

What a great experience, Mary Yonkers .  Will you let us know how it goes?  

Check out the Apple App U.S. Pocket reference. it's free. it has that and more.

 Mary and Dave the kids would be a lot smarter than I am without question.

Mary,
I appreciate a teacher asking the students to be prepared to answer impromptu questions about the Constitution.  Have fun.

Have fun as you judge this contest.

Should be dozens of sites with this download.