The use of "therefor" in my High School Diploma

Solution 1:

At least therefor is a valid word. When these are clear-cut typos (such as "progam" or "graduataion"), this kind of thing can make national news, as it did in Maryland and Nevada earlier this year.

As for your therefor, NOAD labels the word as archaic, with this definition: for that object or purpose. (Archaic language is not uncommon on formal documents; I've seen a few such oddities on some of mine – such as, "In the year of our Lord"). Mirriam-Webster indicates that the definition for therefor is in return for that. OneLook mentions the word is used in legal jargon, and means for that. So, with a simple substitution from these three dictionaries:

Jane Doe has satisfactorily completed the requirements prescribed for graduation and is for that purpose awarded this High School Diploma.

John Doe has satisfactorily completed the requirements prescribed for graduation and is in return for that awarded this High School Diploma.

Jim Smith has satisfactorily completed the requirements prescribed for graduation and is for that awarded this High School Diploma.

Those don't seem blatantly wrong to me. I'd be hesitant about calling it "incorrect," lest the school be tempted to take the diploma back, and not issue you another one. :^)

Solution 2:

Yes, therefor means for that. But (allowing for a bit of slippage over the years) so does therefore. If the sentence read '...has completed a thesis and is [] awarded this diploma', either therefor (in exchange for the thesis) or therefore (because of the thesis) would fit. But completing the requirements isn't really something you can exchange for a diploma, whereas it absolutely is a reason to award one. So, regrettably, I think your High School is in error; it should be therefore.

Solution 3:

I had to read this twice to be sure, but "therefor" is correct here. "Therefore" would probably be correct too.

The sentence means that you are awarded the diploma for satisfactorily completing the requirements. Replace "therefor" with "for that" and you'll see that it makes perfect sense.