You could use an email campaign service, like Customer Minds, MailChimp, Campaign Monitor, etc.
There's a cost to it but it works across all devices and is relatively easy to setup.
Why do you not want to send a PDF?
If it's because people don't open attachments I can understand.
Does you company run wordpress on their server? If so, you could just add all of your people as a subscriber and build the whole thing in HTML and with the new jetpack plugins it will send it correct for small devices too such as iphones and ipads.
Forgive me if this sounds snarky, but you said:
But then you write: "... yet where do I begin?" and "... yet I've not made an online document".
Wouldn't it be a good idea to learn to create on-line documents first, before convincing your company to get rid of PDFs?
Re HTML Newsletters, I agree with Bo, as David Blatner writes:
"The problem with "html email" is that it is dependent on very old email clients. For example, we are having a problem right now that some (but not all) people using Outlook 2003 are having trouble reading the free InDesign Tip of the Week email that we send using mailchimp. Yes, Outlook 2003.
Basically, html email has to be super lowest common denominator HTML. The best html email wouldn't even use CSS, but most email clients can read very simple css now. But remember that later versions of Outlook use MS Word as their HTML viewer, so… it's painful. That means, you really want to use tables and shim.gifs and stuff like that. It's not pretty."