Is the word fold a verb?

Yes, the Word 'fold' is both a verb and a noun.

Examples:

I will fold the flyers for you to stuff the envelopes. (verb)

She hid her hand in the fold of her skirt. (noun)

The last step is to fold the meringue into the batter. (verb)

We're always happy to welcome one more sheep into the fold. (noun)