from: http://blog.sina.com.cn/s/blog_4adf31ea0102e34l.html
MFMailComposeViewController *picker = [[MFMailComposeViewController alloc] init];
picker.mailComposeDelegate = self;
[picker setSubject:@"I have a pencil for you"];
NSString *databasePathFromApp = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"10.pdf"];
NSData *fileData = [NSData dataWithContentsOfFile:databasePathFromApp];
[picker addAttachmentData:fileData mimeType:@"application/pdf" fileName:@"15.pdf"];
[picker addAttachmentData:fileData mimeType:@"application/pdf" fileName:@"16.pdf"];
UIImage *roboPic = [UIImage imageNamed:@"1.png"];
NSData *imageData = UIImageJPEGRepresentation(roboPic, 1);
[picker addAttachmentData:imageData mimeType:@"image/jpg" fileName:@"1.png"];
NSString *emailBody = @"This is a cool image of a robot I found. Check it out!";
[picker setMessageBody:emailBody isHTML:YES];
[self presentModalViewController:picker animated:YES];
[picker release];