I have a document library with an associated workflow. The workflow needs to launch when a new item is created. When adding a new item the form opens, I fill in the fields, and click Save. The form does not close and a message appears at the bottom in red, "The file has been modified by user at time". I have unchecked the Automatically update the workflow state property. This allows me to manually start the workflow. However, when I enable Start workflow when an item is created, the problem returns. Interesting, When I click cancel on the form, the new item is created without the info I fill in the form. Also, the workflow does launch. But without the extra info, it is meaningless.
I think you can enable content types on the document library and then enable Document Information Panel to capture metadata about the document. This should solve your workflow related problem. Have a look here