You can use the System.Net.Mail which has the MailMessage.Attachments Property. Something like:
message.Attachments.Add(new Attachment(yourAttachmentPath));
OR
You can try like this:
using SendFileTo;
namespace TestSendTo
{
public partial class Form1 : Form
{
private void btnSend_Click(object sender, EventArgs e)
{
MAPI mapi = new MAPI();
mapi.AddAttachment("c:\\temp\\file1.txt");
mapi.AddAttachment("c:\\temp\\file2.txt");
mapi.AddRecipientTo("person1@somewhere.com");
mapi.AddRecipientTo("person2@somewhere.com");
mapi.SendMailPopup("testing", "body text");
// Or if you want try and do a direct send without displaying the
// mail dialog mapi.SendMailDirect("testing", "body text");
}
}
}
The above code uses the MAPI32.dll.
Source
It probably won't attach the document because you are at the liberty
of the email client to implement the mailto protocol and include
parsing for the attachment clause. You may not know what mail client
is installed on the PC, so it may not always work - Outlook certainly
doesn't support attachments using mailto.