If you're experiencing problems sending out emails with single-page PDFs attached to them, please make sure your email account signature is not HTML.
You can configure your signature from the Settings.app, under "Mail, Contacts, Calendars" and "Signature".
If the signature shows links in blue, etc, the signature is likely using HTML and that can trigger the email to be converted entirely to HTML and cause some older email clients not to be able to open the attachment.
