Learn Italian: Ho letto il documento, ma non mettermelo nel raccoglitore. - I read the document, but do not put it in the binder for me.

For negative informal commands (telling someone not to do something), you use non plus the infinitive of the verb, which is mettere here. When attaching pronouns to an infinitive, you drop the final -e and stick them to the end, creating mettermelo.

What do the me and lo parts of mettermelo represent?

me means for me, and lo means it (referring to il documento). Whenever the indirect pronoun mi is directly followed by a direct object pronoun like lo, the mi changes to me.

Is it possible to put the pronouns before the verb instead?

Yes! In negative informal commands, you have two choices for pronoun placement. You can attach them to the end of the infinitive (non mettermelo) or place them before the verb (non me lo mettere). Both are perfectly correct and common in Italian.

Why does the sentence use nel instead of just in before raccoglitore?

nel is a combined preposition that merges in with the masculine definite article il (the). Because raccoglitore (binder) requires its article, you must combine them to mean in the.