When creating a document on behalf of a different organization, such as a vendor, make sure you set the Originating Organization attribute to the organization for which it is being created. This attribute is located under the Details tab of the document creation form, under the section 3rd Party Information.
Important: By default, the originating and controlling organizations will be set to your own. Make sure you change the Originating Organization to that of the party for which the document is being created. Failure to do this will result in the other organization being unable to edit the document. In most scenarios they will not even be able to see the document. As the Controlling Organization, you will maintain both read and edit rights to the document. For more information, refer to the section Information Access Control.