This PPTX to KEY conversion does not run here
Keynote is the format a Mac presenter sometimes requests.
Browsers cannot create a .key file.
What to do instead
On a Mac, open the PPTX in Keynote and save it there. If they only need to watch, send a PDF.
The page that does work is PPT to PDF.
PPT to KEY without the extra promises
PPT to KEY sits on this site because PPTX and KEY are not interchangeable, even when they look similar in a file list. Keynote is the format a Mac presenter sometimes requests. Decks are shared as PPTX when the other person will present, and as PDF when they only need to read. People ask for Keynote when a Mac presentation workflow demands it.
Browsers cannot create a .key file.
Read this about PPTX before you upload
PPTX is a modern PowerPoint file. The design lives in the file. A text export only keeps what was written on the slides. Themes, animations, masters, and embedded video are not cloned by a browser tool.
Keep the PPTX. A PDF or Word file of the words is not the deck.
Read this about KEY before you send the download
The download has to be KEY, because that is the format the next step named. People ask for Keynote when a Mac presentation workflow demands it. There is no honest browser path that writes a real Keynote file.
A renamed PPTX is not a Keynote file.
Keep, check, then delete
People lose time when they convert before they know which rule failed. Size, pixel dimensions, codec, font encoding, and layout are different rules. PPT to KEY only addresses the PPTX to KEY step. Keynote is the format a Mac presenter sometimes requests. Browsers cannot create a .key file. On a Mac, open the PPTX in Keynote and save it there. If they only need to watch, send a PDF. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. Do the test with a short or simple file first when the real file is large. A one-page PDF, a single photo, or a one-minute clip will show you whether the output is the kind of file you needed. After that test looks right, run the real file once. Keep both the PPTX original and the KEY download until the receiving person or the upload form accepts it. Slides are a design. PPT to KEY can take the words off them or move a file a browser understands. It does not copy animations, masters, or embedded video. When the deck itself is what you will present, export from PowerPoint or LibreOffice. Use this page for a handout or a format a browser can actually write.
Here is the decision for PPT to KEY. You start with PPTX and you stop when a real program accepts KEY. Slide text can be pulled out for a handout or a transcript. This site cannot produce KEY. PDF or JPG from the slides is the practical handoff. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
On a Mac, open the PPTX in Keynote and save it there. If they only need to watch, send a PDF.
A related step, if you still need one, is ODP to PPT.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.