The question, of course, is 75% of what - their full size or their current display size? Note that, if the images have been compressed and not edited since, their full size is their current display size.
Here's some code that processes all objects (inline and floating) in all StoryRanges to get you started. Extra logic would be required to limit the code's operations to particular types of object and/or to exclude particular story ranges.
Sub ReformatAllObjects()
Application.ScreenUpdating = False
Dim oShp As Shape, iShp As InlineShape, Hght As Single, Rng As Range
With ActiveDocument
For Each Rng In .StoryRanges
For Each oShp In Rng.ShapeRange
With oShp
.LockAspectRatio = True
.ScaleHeight 0.75, False 'True to scale relative to original size
End With
Next oShp
For Each iShp In Rng.InlineShapes
With iShp
.LockAspectRatio = True
Hght = .ScaleHeight
.ScaleHeight = 0.75 * Hght 'Delete "* Hght" to scale per original size
End With
Next iShp
Next Rng
End With
Application.ScreenUpdating = True
MsgBox "Finished Reformatting."
End Sub
Cheers
Paul Edstein
[MS MVP - Word]