Why do PDFs with about the same number of pages differ so much in size?
Themonest reason is authors who don understand how to resize in a document you can drag its edges to make it smaller but it only displayed smaller it still stored at its original large file size. That because the program doesn know whether your readers might want to enlarge it for a better look. If it converted to PDF all that extra information is retained. The remedy is to resize and optimize images before using them and an 8x6 pixel JPG can be reduced to about 3K by a good photo=editing program before the display quality begins to suffer but all the hidden information has been discarded so it can be enlarged. There is a free on-line PDF converter thatpresses PDF files by removing all the extra information that isn needed for display that at smallpdf - dot - - slash -press - dash - pdf which needs reconstructing as Ive had to space the address out so Quora bot doesn mark it as spam. Try it on one of your big files just for fun. Youll be surprised - quite often about 2% of the original size. Back in the 199 when we only had 16 KB dial-up Internet connections everyone worried about file size because a 1MB file would take an hour to download and cost $1 worth of connection time and you couldn do anything else while it was downloading. Plenty of times I had to tell the sender sorry I can receive your file - can you put it on a CD or floppy disk and send it in the mail please? Today generation send each other 1GB files without giving it a thought. Our largest capacity CD in pre-DVD days was 7MB and they cost over a dollar each.