I have personal and Business data spread across 8 external hard drives attached to my main Mac Pro. I have different Projects from the past and present organized on these drives and did not want to move in to my my vault which I also sync with a mac laptop and windows laptop.
So I found if you make a Symbolic link to a Project Folder on i.e HD5 that contains MS office, pdf files etc. And place the Project Folder Link in the vault all files in that folder are available as if they were in Obsidian. The Project Folder Link only points to where the files are actually stored on HD5 not in the vault which saves space. I can add files to the Project Folder on HD5 and Obsidian Project Folder Link updates and shows the new file or I can save an Obsidian note in the Project Folder Link in Obsidian and the md file shows in the original Project Folder on HD5. I can now do normal file links to the Project files in my MOC because Obsidian thinks these are the actual files. And when I click on them they open in excel, word, Omnioutliner, etc. If I know longer need the Folder Link in Obsidian I just delete it and the original files on the external drive are not touched because you just deleted a link. Hope this helps. Like I said above you must use Symbolic Links and not Aliases - Obsidian does not recognize Aliases. Also Obsidian Prefaces the files In the folder link with xlsx, pdf, outline, etc so the linked files are easy to identify.
You can do individual files as links as well but much easier to do a folder as it brings over what ever files reside there.