You can do it with a regular expression , extracting from the URL of the item

Hello Dallas Nix​ -

Is this just one flat folder named "Projects" with a bunch of documents or are there subfolders for the specific projects and that is where the documents will be landing? So something like Projects > Project A > projectA.docx

If the document is going into a folder that is specific to the project, you can update the column in a workflow based on the folder it resides in. You can even set it up so on update it figures out where it is living and updates itself (in case it moves to another project or location).

If the document is just being dumped into one folder with all other project documents, you may want to consider making it a required field upon upload. The drawback with this is it is up to the user to do it, while the other way is automated and predicable.

Hope this helps!