Can't read pdf attachments on zoho mail on ipad

Can't read pdf attachments on zoho mail on ipad

Hi, My boss has an ipad 2 that he travels with. When he accesses his zoho email on the ipad, if there is a .pdf attachment he is unable to read it. If, however, he forwards the same email to his old AOL email, he can open the attachment and read it on his ipad. He has the latest version of his pdf viewer. Is there an issue with .pdfs and the zoho mobile email app that anyone is aware of? Thanks.