The DownsampleColor property determines whether color bitmaps are downsampled when publishing to PDF. You can use the PDFVBASettings.ColorResolution property to set the resolution.
Examples:
The following VBA example publishes the active document to PDF. Color and grayscale bitmaps are downsampled to 72 dpi, and monochrome bitmaps are downsampled to 150 dpi.
Sub Test()
With ActiveDocument.PDFSettings
.DownsampleColor = True
.DownsampleGray = True
.DownsampleMono = True
.ColorResolution = 72
.GrayResolution = 72
.MonoResolution = 150
End With
ActiveDocument.PublishToPDF "C:\MyDocument.pdf"
End Sub