OTTOpen Document Template
Files with OTT extension represent template documents generated by applications in compliance with the OASIS' OpenDocument standard format. These are created with word processor applications such as free OpenOffice Writer and can hold settings that can be used to generate new documents from these template files. These settings include page margins, borders, headers, footers, and other page settings. Such templates are used in official documents such as company letterheads and standardized forms.
Portable Document Format (PDF) is a type of document created by Adobe back in 1990s. The purpose of this file format was to introduce a standard for representation of documents and other reference material in a format that is independent of application software, hardware as well as Operating System. PDF files can be opened in Adobe Acrobat Reader/Writer as well in most modern browsers like Chrome, Safari, Firefox via extensions/plug-ins.