onto/ on to

[Charisse Kitt, CRI CSR RDR FCRR]

I am wondering which one to use in this sentence. I personally think it's two words, but my proofreader sent it back as one word. Please let me know what you think. Tanks! Here's the sentence:

So prior to that time no one had asked you to make sure to hold on to any documents you had relating to the Aroma Program?

[Freddie Reppond]

I'm in agreement with you.

hold on to any documents.

For me, Gregg Reference Manual puts it best: "on" is an adverb in the verb phrase "hold on"; "to" is a preposition.

[Charisse Kitt, CRI CSR RDR FCRR]

Thanks, Freddie. I just wanted confirmation that I was right. I have looked this up every which way, and it is correct, two words. Thanks for your reply.

[Brenda Rogers]

One word. Preposition.

Move on to another project.
Hold onto the moment.