Try using UiPath PDF activities to extract and validate the digital signature instead of UI automation. If the signature is not selectable, use Computer Vision or Anchor Base to detect it. You can also try OCR like Tesseract or OmniPage to extract signature details. If manual interaction is needed, check if “Send Window Messages” or “Simulate Click” works instead of the Enter key. Consider third-party libraries like iTextSharp or Adobe API for signature validation. If the issue persists, take help from the UiPath Support Team.