The Reduce File Size command resamples and recompresses images, removes embedded Base-14 fonts, and subset-embeds fonts that were left embedded. It also compresses document structure and cleans up elements such as invalid bookmarks. If the file size is already as small as possible, this command has no effect.
Whereas Optimized PDF provides many settings for reducing the size of PDF files. Some of the PDF Optimizer settings are comparable to the settings that are available when you create a PDF file using Distiller. Whether you use all of these settings or only a few depends on how you intend to use the files and on the essential properties a file must have. In most cases, the default settings are appropriate for maximum efficiency—saving space by removing embedded fonts, compressing images, and removing items from the file that are no longer needed.
Let us know if you have any further query.
Thank you for your very comprehensive answer!
1 person found this helpful
There is one other important difference: "Reduced Size PDF" is available in both Acrobat Pro and Standard, whereas "Optimized PDF" is only available in Pro. When you are using "Optimized", you can also use the "Audit space usage" feature to find out which elements in your PDF file are using up what amount of space. This helps to fine-tune your optimization settings.