need: Re-sizing a pdf for a client

My need is to take an existing pdf, say of letter size original, and make it a larger or smaller pdf document. I am not referring to "viewing" it larger or smaller, which is the only information I find when I search the term: re-size.

End product needs to be the same content, just different size, yet still editable as far as copy.

If it makes any difference, I am Mac based.

many thanks,

Catherine