1. Check the recipient’s mail settings to see if their mail client can read .pdf files.
2. If the recipient’s mail settings do not support .pdf files, resend the message as an HTML file or OpenDocument Text file, or include the content as plain text in the body of your email message.
3. If the size of your attachments exceeds the maximum message size set by the recipient’s mail server, try removing any non-essential parts of the attachment or using a file compression tool such as WinZip before sending it.
4. Consider using an online file storage service, such as Google Drive or Dropbox, to transfer large file attachments.