If this is the typical setup where the main form contains records and the
subform has only the matching records, it is not just a matter of applying a
filter to the subform. What you need to do is to filter the main form so it
contains only those records that have a match in the subform.
If that's what you are trying to do, see:
Filter a Form on a Field in a Subform
at:
http://allenbrowne.com/ser-28.html
If the subform has nothing in its LinkMasterFields/LinkChildFields
properties, then it is just a matter of applying a filter. You could put an
unbound text box on your form, and use its After Update event procedure to
filter the subform:
Private Sub txtFindThis_AfterUpdate()
With Me.[NameOfYourSubformControlHere].Form
If .Dirty Then
.Dirty = False
End If
If IsNull(Me.txtFindThis) Then
.FilterOn = False 'Nothing entered: show all records.
Else
.Filter = "[Subject Keyword] Like ""*" & Me.txtFindThis & "*""
.FilterOn = True
End If
End With
End Sub