This suggestion of giving the users the ability to compress/optimize PDF files to reduce file size, applies to the ONLYOFFICE Desktop Editors app Windows version

Within the app I did not find a feature to compress/optimize PDF files in order to reduce file size.

Other competitive apps such as: Adobe Acrobat Pro, Qoppa’s PDF Studio Pro, PDFgear, Wondershare’s PDFelement and Foxit PDF Editor to name a view, do have such a feature that can shrink PDF files and reduce their file size, without having to remove any page or other necessary content (e.g. images) that needs to stay in place.

Please see the uploaded/attached screenshot files taken from the mentioned competitive apps and where applicable from their User Manuals.