An OTP file is a presentation template created by Impress, a program included with Apache OpenOffice (formerly known as OpenOffice.org). It contains a presentation, which includes a master slide as well as a content slide with text, images, shapes, multimedia content, transition effects, and other slide elements. OTP files are used for styling presentations with the same appearance.
OTP file open in Apache OpenOffice Impress 4.1.3
OTP files may also be created and opened by presentation software that supports the OpenDocument standard. However, most OTP files are created by Impress, which is one of several programs available in the OpenOffice suite. It is similar to the PowerPoint program available in the Microsoft Office suite. Many users who need an application like PowerPoint but can't afford the cost turn to Impress and OpenOffice as a free alternative. The OTP file is used by Impress to save a template of a presentation the same way that PowerPoint saves a template of a presentation in the .POT or .POTX file. OTP files are based on the OASIS OpenDocument standard, which uses an XML format to save presentations.
You will most likely only see the OTP file if you use the Impress application or if another OpenOffice user shares a presentation template with you. Examples of templates include family photo slide shows, school reports, and financial summaries.