unlock a locked word 2007 document:

unzip the file

in docProps/custom.xml, which looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Properties xmlns="http://schemas.openxmlformats.org/officeDocument/2006/custom-properties" xmlns:vt="http://schemas.openxmlformats.org/officeDocument/2006/docPropsVTypes"><property fmtid="{D5CDD505-2E9C-101B-9397-08002B2CF9AE}" pid="2" name="_MarkAsFinal"><vt:bool>true</vt:bool></property></Properties>


change that property value from true to false, like so:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Properties xmlns="http://schemas.openxmlformats.org/officeDocument/2006/custom-properties" xmlns:vt="http://schemas.openxmlformats.org/officeDocument/2006/docPropsVTypes"><property fmtid="{D5CDD505-2E9C-101B-9397-08002B2CF9AE}" pid="2" name="_MarkAsFinal"><vt:bool>false</vt:bool></property></Properties>


save the file and zip up the document again.