While editing a kahoot, click on the "Add slides" button and then select the "Import slides" option on the pop-up window to import slides from a PowerPoint (.pptx or .ppt), KeyNote (.key), or Adobe PDF (.pdf) file.
You can upload files as large as 80MB. Please note that a single kahoot can’t exceed 100 questions (each slide counts as a question).
Are your slides in a Google Slides deck? No problem! Just download them as a PDF file. This is done via the following menu path: File > Download > PDF Document.