It was one of the most annoying aspects of storing a file in Account Engagement (Pardot), and rather hard to justify to someone who was unfamiliar with the peculiarities of the system.
Me: "When you access a file, the browser just downloads it to your computer"
Client: "Why? I want it to load in a browser tab. Can't you make it do that?"
Me: "No. It's for ahem, [best excuse I can use with a straight face] 'backward browser compatibility'" I'm happy to report, however, that we finally have a solution to this conundrum. Salesforce quietly issued this update last week. Now files accessed will appear in a browser tab when loaded, instead of downloading!
Except when they won't....
The important detail in here is that this behavior will only apply to files uploaded on or after January 23, 2023. So all your old files will still retain the legacy behavior if you do nothing. But don't fret, you don't have upload new and re-link everything. Here's the most efficient way to fix this on any files you want to open in the browser without risking breaking anything.
Download the existing file from the existing Pardot File link.
Use the Edit feature to replace the file with the file you just downloaded. Just upload it again.
This changes nothing with the file link but changes the behavior to loading in the browser.
While you're at it, this is a great time to audit your files for dead content or never-viewed content. Just check this "Last Viewed" column (itself a fairly recent addition) to see when the file was last accessed. Just make sure you do this before you make your updates, because they will show up as an access. You may find that some files have never been viewed at all, and you might be better off cleaning them out than updating them.
This is also a great time to consider adding conditional completion actions to file access. Yes, you can use conditional actions on file access now! The ability to see file accessed and apply completion actions is one of the best arguments for storing files in Account Engagement, instead of somewhere else. This change to the default behavior removes one of the most common objections to storing documents on-platform. This is also a good reason to store documents in Files even if you are using the new Lightning Email Builder. Simply copy and paste the link instead of choosing it from the CMS.
UPDATE: Firefox Blocks Pardot File Downloads
Since this article was published, a new build of Firefox is blocking by default the old downloading behavior, so re-uploading your older document files that are still commonly used takes on new urgency if you have a lot of visitors that are Firefox users. I've also written an article on how to bulk download all your Account Engagement files to make this task just a bit easier.