You can use either custom document properties or document variables to
hold the user's values. The main difference between them is that
custom document properties can be set in the File > Properties dialog,
while document variables can be set only through VBA. A less important
difference is that doc properties can be created with different data
types (string, integer, boolean) while doc variables are always
strings.

Once you choose your weapon, insert either {DocProperty} or
{DocVariable} fields in the body of the template, referring to the
properties or variables. You can have more than one field referring to
the same property or variable, and those fields will all show the same
value. (If you insert the fields before the props/vars exist, they'll
display an error message. You do need to create the props/vars in the
template before you distribute it.)

Write your userform so that the cmdOK_Click() procedure first
validates all entries on the userform and then places the values from
the controls (textboxes, checkboxes, comboboxes, etc) into the
corresponding doc properties or doc variables. The last thing is to
update all fields in the document, so they'll show the new values.

In the Userform_Initialize() or Userform_Activate() procedure, read
the values of the doc props/vars and put those values (if they exist)
into the controls on the userform. That way, a document that's being
re-edited will initialize the controls to the previously entered
values.

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Regards,
Jay Freedman
Microsoft Word MVP         FAQ: http://word.mvps.org