I was wondering whether it's possible to attach a file with a campaign? Or do I have to upload said file and just link it?
Attachments aren't possible. You'll need to host the file somewhere and link to it from your campaign instead.
I'm a little late to this thread but we just integrated with Campaign Monitor to allow you to easily send files inside your CampaignMonitor newsletter: https://digioh.com/campaignmonitor
One of our coolest features is if a file gets forwarded on we will prompt them to signup to your newsletter before they can download your file.
Let me know if you or anyone on this thread has any questions.