Symbols | Symbols Library and Document Name

Okay, 

I have a question regarding Symbols. 

1. Where are the named .cdr Symbols saved? I ask because for each saved & named .cdr  I open it contains it's own Symbols. These symbols are not located in the General Symbol Folder. So where are they? 

2. How are these symbols linked to show up in the .cdr's Symbol Library when I open the named .cdr file? 

I ask because....

Our website allows customer to upload their own artwork via our website. We'd like to link this artwork file to the .cdr that was also automatically created and named. Our plan is to have this artwork file display in symbols library when the .cdr file is launched for immediate use! 

I assume we'd have to change the extension of the uploaded artwork file. Place it in the location where the .cdr's symbols are?

Is this possible? I realize some files wont work. Aside from that. Can this be done? Can an example be given?