Windows – Microsoft Word restores all open documents when clicking on a .DOC file

If there's a check mark on the option Tools > Options > Print > Update fields (in Word 2007, Office button > Word Options > Display > Update fields before printing), then going to Print Preview and back will update the fields. But it's just as easy to press Ctrl+A and then F9.

If you're looking for something that doesn't need any user interaction at all, then you need a macro.
An example of a macro to update all fields of type ToC is:

Sub TOCFieldUpdate()
' Written by Charles Kyle Kenyon 27 January 2005
' Field Updater - TOC fields
Dim oField As Field
On Error Resume Next
For Each oField In ActiveDocument.Fields
If oField.Type = wdFieldTOC Then
oField.Update
End If
If oField.Type = wdFieldTOA Then
oField.Update
End If
Next oField
End Sub

If you wish to periodically execute the above macro, here's another macro for that.
that will update the ToC every 5 minutes:

Public Sub ToCUpdate()
Call TOCFieldUpdate
DoEvents
Application.OnTime When:=Now + TimeValue("00:05:00"), name:="ToCUpdate"
End Sub

You can assign this macro to an icon or a hotkey. I wouldn't suggest to make it run automatically when the document opens, as you would run against the latest security safeguards of Microsoft.

Note: The above is untested, and even worse, is my very first attempt in writing VBA.

If there are images in the RTF document, you may want to check out this KB article from MS:

Symptom blurb:

...If an EMF, a PNG, a GIF, or a JPEG graphic is inserted into a Word document, when the document is saved, two copies of the graphic are saved in the document.

...a Microsoft Word 2000 document that contains a JPEG graphic that is saved as a Word 2000 document may have a file size of 45,568 bytes (44.5KB). However, when you save this file as Word 6.0/95 (.doc) or as Rich Text Format (.rtf), the file size may grow to 1,289,728 bytes (1.22MB).

Resolution blurb:

To prevent Word from saving two copies of the graphic in the document, and to reduce the file size of the document, add the ExportPictureWithMetafile=0 string value to the Microsoft Windows registry...

Maybe there's some help there?