As the Product Manager for Google Docs, facing a 10% decrease in the 'Open' metrics, what steps would you take to investigate and address this decline?

Focus on a structured approach to diagnosing the decline in 'Open' metrics for Google Docs. Start by identifying potential data sources and user segments that could provide insights into the drop. Consider both qualitative and quantitative methods, such as user surveys, usage analytics, and A/B testing. Discuss how you would prioritize potential causes, like changes in user behavior, competitive landscape, or product updates. Finally, outline specific actions you would take to address the issue, including potential feature enhancements or marketing strategies to re-engage users.