If you have Acrobat Pro you can do it with an Action.
Please navigate to the tools pane and type "Action Wizard " in the search box and select action wizard from the list .
Then , select the option "Optimize for web" and select the option "Add files" .
You can add multiple files you want to optimize and click on start and the files would be optimized .
Let us know if this helps.
I use tools -> action wizard -> Optimize Scanned Documents -> drop down menu and select files or folder of PDFs -> then under enhance it will say " add document description" it will be greyed out, but it still does it, yeah right-click on that and select skip. -> now tell it to save as or overwrite it with save and it will process the whole thing without interruption. It will take some time, so go make a sandwich.