Hi,
We are using version 17.6 for now, can I know what is the solution for saving size when merge lots of pdfs which got same image in same position?
First of all, please try to use the latest version of the API as you are using quite older version and a lot of changes have been made in the API since then. Furthermore, once all PDFs are merged, you can optimize size of the final document by removing duplicate image streams and other resources as mentioned in below article(s):