Smartsheet would be a better project management tool if it would allow a document that is attached to any line item to be editable within the tool (instead of the current keystrokes of downloading it, editing it, and then uploading a new copy). Because Smartsheet does not allow this feature, we do not use the tool for as much as we could.
If you host the attachment on a cloud platform (one drive, google docs, etc..) instead of uploading the file to smartsheet, then this (kind of) already works.
If we want the file to be READ-ONLY, we upload the file directly.
If we intend to edit it as a group, we upload it to one drive.
In the image below, the first attacnment is hosted on OneOne Drive. Other users can edit that file in their browser (based on permissions).
The second file would have to be downloaded, edited & then re-uploaded.
This starts a whole other mess of issues with poermissions, though. The permissions of One Drive need to match Smartsheet. And, if you move the file in the One Drive it breaks the link.
Not perfect, but might get you where you want to go right now.
Thanks