.pptx files are created and opened using Microsoft's PowerPoint (2007+) application. The .pptx file format is a newer version of the original PowerPoint format, and now included compression to reduce file size and is based on XML architecture.
PowerPoint is a presentation program and is mostly used for displaying digital slides during business/educational presentations and is also widely used for displaying picture slideshows received by email.
PowerPoint belongs to the Microsoft Office suite and is available for both the Windows and MAC OS operating systems. PowerPoint is now arguably the standard way of displaying slides, making the slide projector virtually redundant.
The .pptx file can contain a combination of text, pictures and even movies. These files are all held within the actual .pptx file, so you only have one file to distribute or receive. The .pptx file also holds information on how the presentation is displayed, such as the transition effects between slides.
PowerPoint also saves presentations in .ppt (presentation), .pps (presentation) or .pot (template).
To create/open a .pptx file, you will need PowerPoint (part of Microsoft Office suite) or PowerPoint Viewer 2007, which is available free from Microsoft's website (link below).