Newb Question Regarding Gpg4win Privacy

I’ve been reading the very well written Gpg4win Compendium, and I read the following in Chapter 8:

“To exchange secure e-mails, both partners must have and use the public certificate of the other person. Of course the recipient will also require a program capable of handling certificates – such as the Gpg4win software package with Kleopatra certification administration.”

Does this mean that, in order to send truly private emails, each of my contacts have to be using Gpg4win as well? Are my emails encrypted if I send them to someone not using Gpg4win? Thanks in advance.

Maybe not exactly gpgwin, but some application handling openpgp format will be required.
If you send email to someone not using gpgwin (or any other application handling openpgp format), it is most likely unencrypted. (if it was encrypted, recipient would not be able to decrypt)