arcpy.mapping - 'ExportToPDF', 'ExportToEPS', and 'DataDrivenPages.exportToPDF' - image_compression needs to default to 'Adaptive'. Also, add 'JPEG' option and control for JPEG quality.
Use named arguments like the following.arcpy.mapping.ExportToPDF(mxd, "<a href="file:c://text//out.pdf" target="_blank">c:\\text\\out.pdf</a>", resolution=300, image_compression="LZW")