Assuming by files you mean drafts and not file system files, you could use a an action with a single script step and content like this.
Just substitute in the UUID of the draft you want to open, and set your preferred keyboard shortcut.
If you want to load a file in a particular application from the file system, that perhaps depends on the files, OS and the apps as to potential approaches. Some apps have URL schemes where you can direct them to a file. If you are exclusively referring to the Mac, you could trigger a shell script from a Drafts action that could open the file. If you’re one i*OS, maybe tying it into a Shortcuts shortcut might be an option if the app has good Shortcuts support. If you want to import the file each time into Drafts, you have other options too.