State Employee Wants to Publish Self-Authored Guide

Dear Rich: I work for a state agency, and as part of my job duties several years ago, I wrote a guide. The guide was not copyrighted, is in the public domain, is available only as a pdf, and has never been printed. I am the sole author, and am noted as such on the title page. My question: I am retiring soon, and may want to update and expand the guide. Is it legal for me to have the guide printed as is and to sell the print copies? If I revise and expand the guide, would it be legal for me to copyright and sell it? We're not sure why you have concluded the work is in the public domain but if it is, you're free to do what you wish.
Who owns what? It sounds as if your employer owns copyright under work made for hire principles -- that is, it's a work created in the course of employment. Unlike works by federal employees, works by state employees are not in the public domain although some states such as California and Florida do place state-produced works in the PD.
Is it public domain? When you say the guide is "not copyrighted," do you mean it was not registered with the Copyright Office. Filing a registration is recommended but it's not essential for protection.