PPTX and why it is used
PPTX is the modern PowerPoint file format, introduced with Office 2007 and used today by PowerPoint, Google Slides, Keynote and LibreOffice Impress. When a teacher, trainer or manager needs to show a PDF on a projector, add commentary between pages or reuse pages in an existing deck, a .pptx file is the most practical format.
What happens when you convert
Each page of the PDF is drawn at double resolution and placed on its own slide as a sharp picture. The slide size is taken from the first page, so the pages fill the slides without being cut. The .pptx file can be uploaded to Google Slides or opened directly in PowerPoint and Keynote.
Working with the slides
Use the converted slides as a base: insert your own title and summary slides, add arrows and highlights over important parts, write speaker notes, and set transitions. The text in the page pictures cannot be edited, but anything you add on top stays fully editable.
Common problems and how to fix them
You need editable text on the slides: copy text from the PDF with PDF to Word, then paste it into new text boxes. Small text is hard to read on a projector: zoom into the important area by cropping the picture in PowerPoint. The presentation is large: delete pages you will not show before converting.
Good habits
Keep the original PDF as a handout, test the deck on the actual screen before presenting, and save your edited deck under a new name.