PPTX is a more modern and convenient presentation format in the popular Power Point application, which replaced PPT after entering the Microsoft PowerPoint 2007 market in updated office suites. Full name - Microsoft PowerPoint Open XML Document. Designed for the same purposes as PPT - creating a presentation in an editable slide show format. The difference from the first version is that the PPTX file is created using the open XML format. If in the PPT format the data is stored in one binary file, then in the PPTX format - in a compressed ZIP archive as a collection of separate files.
PDF is short for Portable Document Format, which can be translated from English as “Portable Document Format”. It was developed by Adobe Systems for use by US federal authorities as a tool for storing working documents. This is a universal cross-platform format, which is now standard for electronic documents. It serves to convert text files (including photographs or other images) into electronic documents without any loss. To read PDF files you need special programs - Adobe (Acrobat) Reader, PDF-Viewer and others.