When you save a document as .doc from Open Office, you indeed convert all fields to plain text. If you must save as .doc from OpenOffice, use the "Bookmarks" option under "Set Document Preferences", though if at all possible we recommend sticking with Reference Marks and using Ooo's native .odt format.

yes, that's exactly what I was answering.

When you click on "Set Document Preferences" what do you see? If Bookmarks is greyed out, you can't use it (that's the case for styles using endnotes or footnotes)

it's part of the Zotero toolbar in Open Office. https://www.zotero.org/support/word_processor_plugin_usage#plugin_toolbar