Link to a Dropbox File
Preceden does not support file uploads, but you can store files in another cloud service and link to them from your event notes.
Here's how to do that with Dropbox:
1. Get a link to your file
If you're on a Mac, you can right-click the file name in Dropbox and click Share...:

(The process is similar on Windows and in the Dropbox web app.)
Next, click the Create Link icon:

Dropbox then creates a link to the file, and Copy Link puts it on your clipboard:

The URL will look something like this:
https://www.dropbox.com/s/01mt4kn66ohwrr7/Meeting%20Notes.pdf?dl=0
Anyone who knows this URL can open your file, but in practice the URL is impossible to guess, so the file stays private unless you share it with someone (by linking to it from a Preceden timeline, for example).
2. Add a link to it from an event
You can then add this as a link from your event notes in Preceden.
For example, this Markdown gives the link a name:
[Download Meeting Notes](https://www.dropbox.com/s/01mt4kn66ohwrr7/Meeting%20Notes.pdf?dl=0)
And Preceden displays it like this:

If you run into any issues, don't hesitate to reach out: [email protected].