Hi there! I see you're having trouble sending a PDF to a recipient via email. Could you tell me a bit more about how you’re trying to send it? For example, are you using a specific PDF app’s “Send to Email” feature or attaching the PDF manually in an email client like Outlook or another mail app?

In the meantime, here are some general steps to start troubleshooting the issue on your Windows 10 device:

1. Update Your PDF App: Make sure your PDF reader or editor app is updated to the latest version. Sometimes bugs that affect email sending are fixed in updates.

2. Check Default Email Client Settings: The “Send to Email” function often relies on the default mail application on your computer. If the default mail app is not set or misconfigured, the PDF app might not open your email client properly to send the file.

3. Try Manual Attachment: Instead of using the “Send to Email” button in your PDF app, save the PDF file to a local folder on your PC. Then open your email client (such as Outlook) and attach the PDF manually to a new email message.

4. Restart Your Computer: Sometimes, temporary glitches with your email or PDF apps can be resolved by a quick restart.

5. Check for Error Messages: If you get any error messages when trying to send the PDF, those can help pinpoint the problem. Please share any such messages if you encounter them.

Let me know which PDF app and email client you are using, and if you tried any of these steps already. I can guide you through more targeted troubleshooting from there!