I had to send out a corporate communication the other day. I wrote it in Word, with some words and a few little graphics (flags, screenshots, and so on). Came to 148K, which I thought was pretty good. As I had to email it to all staff around the world, I figured I cared about the file size - even if the email server is clever enough to keep one copy and a load of links, because we use Notes (which replicates to local copies on people's laptops) we do have to have one eye on file size.
I hit "Save as PDF" ... and ended up with a half-meg file. As it was an internal document and I don't care about people being able to edit it, I figured "sod it" and sent the Word version that was a quarter of that size.
The moral of the story: don't just assume PDF will be an efficient way to send stuff around - at least not without tweaking the custom options!