I used Aspose pdf(dll file version: 126.96.36.199) to save each image in the pdf to file then replace the image in the file with the new saved ones.
XImageCollection xImageCollection = p.Resources.Images;
XImage xImage = xImageCollection[index];
using (FileStream imgFile = new FileStream(outImgFile, FileMode.Open))
p.Resources.Images.Replace(index, imgFile, imgQuality);
The expected output image should be processed and have the same look with the input image, however the color changed to greyscale, and the check box is turned into black-filled. Please check my attachments for more details.
Converted.pdf (164.2 KB)
Original.pdf (144.7 KB)