You can try using Alcohol, if you put some on a cotton swab if you dab you should see it start to come up, it works for regular pens, so I don't see why it wouldn't for gel pens, just be careful not to put to much so you don't ruin your documents. and use my advice at your own risk.
Gel pen ink is supposed to be extremely hard to remove. Most regular ink stains will come out with rubbing alcohol. But gel pens are what they recommend to use to write checks with as the scammers who steal mail and then "wash" the checks with chemicals to remove the ink can't when it is a gel pen. Even their solvents won't lift the ink!
I don't know what brand your pen was. You could look up the manufacturer's website to see what they recommend. On the website for Uniball pens I found this:
The Removal of Stains for Pens from Uniball's Website
To remove most stains from most surfaces, Sanford recommends you try Ammodex ink and stain remover. Amodex is not sold in stores. You can call them for more information at (203) 335-1255.
Your best chance at complete stain removal with all Sanford inks on all surfaces is to use Amodex! It removes virtually any ink or food stain on virtually any fabric or surface. Best of all, it will work as well after two weeks as it will after two hours - so it is probably worth the wait for your favorite or expensive garments. If you plan to use Amodex, do not attempt to treat the stain first - even rinsing in water can reduce the solution's effectiveness.
It isn't available in very many stores and appears somewhat pricey.
Their website is:
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