I need to learn more options for reducing file size on pdf files.

I am working with very old books, I have tried both the option to "reduce file size" and "optimizing". I have also been trying to fine tune a custom - optimized setting to reduce file size with no success. The files are old books dating from the late 1800's to the late 1960's. I am having no luck in either end of the age spectrum. The books contain B&W photos, graphs, and text. It appears that the text is treated as an image. Adobe recognizes the old text as Times. I am not experiences in this, but have learned the basics from a few tutorials. On a separate note: Can a change to the driver, effect pdf file reducing capabilities? I successfully reduce one of these files from 34.9 megabytes to 3.79 a few months ago and cannot replicate it. I am lucky if I can get 1 to 2 megabytes to compress in my recent attempts. My organization is regularly changing the drivers on our system.

Anne Marie Van Coesant