In sharepoint, You have to add that field to that document Content Type. If It's not selected in Content Type then it can't be used as DocProperty.
Open your document template from Sharepoint and in your Header or Footer from Word do following:
1. On Quick Parts, select Field.
2. From the list of Field Names, select DocProperty
3. Click the Options button, select Version in the list of available Document Properties, and click the Add to Field button
4. click OK twice to insert the field.
This way you can retrive any info from Properties to your document.