What you've done is OK and pretty quick, and if you want to stop any of your learners copy your text it will counteract that too.
However, it's not a great way of putting in text and graphics - for a start, the image is a fixed width and height so won't repaginate when users move their browser window about, neither will it adjust for different screen widths. The lesson screen automatically adjusts to fit the browser screen, offering the learner better viewing/reading.
Iframe will work too, but again it won't adjust. Iframe is best to import fixed width items (such as flash .swf files etc). It will act similarly to inserting your pdfs as a image in this case and although it's very simple, it means an extra little bit of work on your behalf in each page - so out of the two I'd recommend you stick with image inserts.
Do you have most of your content in Word? You cannot copy straight from Word into a lesson (well, actually you can but it really stuffs up all the formatting and adds tons of erroneous code. Even the option in the editor to scrub Word text isn't infallible). If you're going to do a few lessons in the future I'd recommend that you persevere with formatting text. Once you get the hang of it - and it's pretty intuitive - it'll be quick. Copy your text from Word and paste it into Notepad or Wordpad to change it into plain text. Paste that into the lesson screen. You can plan to use only a few formatting changes - keep all font size the same (so you can select and change all) for instance. This will keep your time down.
Then, with your images (PNG is best, if you can) upload them all in bulk to the course folder, rather than import them through the editor. This will be infinitely quicker. If you don't know how to do this either reply to this post or send me a message and I'll give you brief instructions.
It'll be worth learning - you'll get better results. Your learners will be able to read it better on screen and you'll have another Moodle skill to add to the list.