While preparing an online report for the PUT1107 project, I encountered a limit for uploaded pdf-files as low as 3 Mb. Thus, I was forced to reduce the pdf-file size to this limit as follows:
1. I merged a set of articles into one files: pdftk 1.pdf 2.pdf 3.pdf output set.pdf
2. Then I reduced the size of the resulting file: gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=out.pdf set.pdf
The size was reduced by more than 50% with almost the same visual quality.