An online system stores online documents, where each online document has a layout. The system creates augmented online documents by combining the online documents with one or more content items. The system stores client interactions with the content items, responsive to presenting the augmented online documents via a client device. The system receives a new online document. The system creates new augmented online documents by combining the new online document with one or more new content items. For each new augmented online document, the system generates a score based on one or more features describing the layout of the new augmented online document. The system selects a new augmented online document based on the generated scores and sends the selected new augmented online document for presentation via a client device.