Creating a complete responsive digital signature tool with HTML, CSS, and JavaScript can be a complex task that requires a significant amount of code. Here, I'll provide you with a simplified example to get you started. You can expand and customize this code as needed:

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Digital Signature Tool

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In this code, we have created a simple digital signature tool with HTML, CSS, and JavaScript. It includes the following features: 1. A canvas for drawing the signature using the Signature Pad library. 2. Clear button to clear the signature. 3. Download button to save the signature as an image. You'll need to include the Signature Pad library using the provided CDN link. This code provides a basic starting point, and you can further enhance and style it to meet your specific requirements.