I've actually found one called "textstat", but it doesn't recognize different word forms of one word.
So are there programs that do detect comía, come, cómelo, comiera as forms of comer?
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You can try the Spanish stemming algorithm found at http://snowball.tartarus.org/algorithms/spanish/stemmer.html.
These are more intended for spelling-correction. However, since they also try to grok the conjugations and flexions for languages with them, they could be helpful. These programs expose an interface so you can call them from other programs (such as a word processor or a browser), you could create a script that reads your text file and calls it continuously not for the sake of spelling but to get the "base" word ("comer" in your example)