"Do I send this and when?"
Once you've circulated and edited the minutes with your CEO and Chairman, it's time to send it via email to all board members to have a look. They can comment and propose changes before the next meeting when it will be signed.
"PDF or DOCX"
I would always send out a PDF as it's much easier to open on a mobile phone. Remeber to make all your board documents mobile friendly!
"Do I send it to everyone on the participant list?"
It's good to share the minutes only with the board members, as they will be signing the document. Note that you'll only need signatures from enough members to have a quorum.