https or encryption + mail

I would like to send email securely using free Yahoo mail

Additional Details

I would like to able to send information to companies, on an
occasional basis, where it would be best if the information was
secured.

What is needed is something simple where the companies can easily read
the mail.

For example, if I could encrypt the message attachment and they could
click on it, provide a password, and then read the mail.

Since the companies know my email address, it would be necessary for
me to use my usual web mailer.

Thanks

Ps. The facility should be free
.