This is a really basic question that I'm sure everyone else knows the answer to but I'm not that techie.
I have a file on my PC that I attach to a note in Joplin. If I edit it in Joplin will it be updated at it's original location on my PC?
Alternatively, if I edit the original file on my PC does the attachment in Joplin reflect this?
Finally, if I edit the attachment in Joplin on my phone, does it update the original file on my PC?
The answer to both - it depends on how you attach the file. If you copy it to Joplin, which I think is the default way, then there's no connection between the original file and the attachment and the answer to both questions is "no".
You can (at least on desktop) put a link to the file on disk in Joplin. Then you can still edit the file outside Joplin but the price you pay is the file won't be synced.
If you attach a file using the Joplin toolbar or drag-drop and the link looks like this [Demo.docx](:/339a34e05cd4488bb85c1e6b079fa7a9). Joplin has placed a copy of your original file, as it was at that time, into its store (/<home folder path>/.config/joplin-desktop/resources) and given it its own unique reference to keep track of it and sync it (339a34e05cd4488bb85c1e6b079fa7a9). If you later edit the original file on your computer any changes will not be reflected in Joplin's copy as they are now two separate things. However if you open the copy stored in Joplin by clicking on the link in a note it will open the file in the default editor for that file type. An orange banner will appear telling you that the attachment is being "watched" for changes. If you make any changes whilst Joplin is watching and save that copy, the changes will be stored and, as Joplin knows that the attachment has been updated, the updated attached file will be synced and all connected devices will get the updated copy. The original file on your computer remains unaltered as you performed the edit on Joplin's copy it stores in its resources folder.
If for some reason you found the file in the Joplin resources folder and edited it directly the edited file would not be synced as Joplin was not "watching" when you did it. Attached files (stuff in the resources folder) either on your local machine or on any cloud storage used for syncing should not be directly edited. Joplin would not know of the edit and so would behave as if nothing had changed.
A less common method is if you manually link a file on your PC to Joplin using a link similar to [Demo.docx](file:///C:/Users/Username/Documents/Demo.docx) (ALT + Drag-drop). This is only a link to the file on your computer. If you edit the file on your computer you will see the changes if you click the link in Joplin as it is only a link to the file on your computer. The linked file is not synced and is not controlled / monitored by Joplin. Joplin knows / cares nothing about this file, only the link text in the note. The note containing the link text will be synced but clicking on that link in any other client will not open the file as it is not part of the Joplin sync. Also, in the case of the example Windows filepath above, it would be a meaningless filepath on a Linux / Mac computer or Android / IOS mobile.
I do not believe that you can edit attachments on mobile.
Thanks.
So, to properly utilize Joplin (or Evernote and other similar apps I assume) I have to put what ever information I want in Joplin and then only access it from Joplin? I wouldn't ever touch the original file on my PC?
If Joplin was destroyed by aliens tomorrow, how would I access my information that was stored in Joplin?
If aliens have destroyed Joplin but have been nice enough to leave your profile intact, you can always get the info from there. Assuming the aliens didn't also destroy SQLite, you can open your database with it and easily export it. The app also lets you export to open formats like Markdown or HTML so in that way it's safe too.
Yes. However attachments are there as a way of adding a bit of extra, likely non-text, information to a note. Joplin is not a document management system.
Install the backup plugin and automatically back it all up to somewhere safe and out of the reach of Joplin-hating aliens.
I still can recover my Joplin database from synced cloud services (such as OneDrive, Dropbox and WebDAV) or local folders in case of Joplin was destroyed by aliens. On the other hand, a CEO can easily destroy Evernote, Keep, OneNote, Synology Note or other services (See what happens to Google Photos) at any time. That's why I choose Joplin since it is probably a life-time note keeper.