Hi
In this case, I think you could not use document URL. Document URL can only be used for document which is stored external and you know the link to access to it.
In this case, I think you can :
1. Upload the document to the folder where your EDocman documents are stored .
2. Go to EDocman -> Configuration, set "File Upload Method" config option to "Choose file from server"
3. Now, create new document, you will see the file listed in the files dropdown and you can choose it for your document.
That should solve your issue. Please try !
Tuan