I am trying to create a PDF document that includes many images. All of them are on the foreground except one, which is a monochromatic background and spans the whole document area. I found that without the background, the PDF file size (single page) is around 10MB, but with the background, the file size can go to 20-30MB.
What I would like to do is to reduce the PDF file size. Since the foreground images need a high resolution (~300dpi), I don't think I can do much about them, so I would like to ask if there is anything I can do to the background image before or after creating the PDF. I tried to reduce the resolution of the source image before adding to the document and converting to PDF, but the reduction in PDF file size is quite minimal. I wonder if I can take any advantage of the monochromatic nature of the background image, or whether I can use some software to selectively optimize the background after the PDF is created. Thanks!