Learn Italian: Potresti mandare il file a Marco? - Could you send the file to Marco?

Potresti is the conditional form of potere (can/to be able to), meaning "could you". At this level, you will see the conditional used a lot for making polite requests. Puoi mandare means "Can you send", while potresti mandare is a softer, more polite "Could you send".

Why is "mandare" in the dictionary (infinitive) form?

Because it follows potresti, which is a modal (helper) verb. In Italian, when you use a modal verb like potere (can), volere (to want), or dovere (must), the main action verb that follows it stays in its infinitive form.

"File" is an English loanword. Do foreign words have a gender in Italian?

Yes! Foreign words adopted into Italian are almost always treated as masculine, which is why it uses the masculine article il, making it il file. They also do not change their ending in the plural, so "the files" would simply be i file.

Could I use "per Marco" instead of "a Marco"?

It would change the meaning. A Marco means you are sending the file directly to him as the recipient. If you said per Marco, it would mean you are doing the favor of sending the file on behalf of Marco, or that the file is intended for him but sent to someone else.