Created the parent doc type table and altered all the profile search screens and maintenance screens.
Need to put the old doc types under a parent doc type so created an 1_OLD parent document type (the "1_" so it will be listed first in a lookup). Looked up the SYSTEM_ID of the 1_OLD parent document type and used this SQL command in SQL analyzer
update docsadm.documenttypes set PAR_DOC_LINK = '295778' WHERE PAR_DOC_LINK is null
to change all the old document types so they will be children of this parent document type.