PowerPoint to Word is a transcript, not the slides
Same job as PPT to Word: get the words off the slides.
Each slide's text becomes a section in a Word document.
Animations and masters
You do not get a designed handout. For that, use PowerPoint's own handout export.
Why PowerPoint to Word is its own job
PowerPoint to Word sits on this site because PPTX and DOCX are not interchangeable, even when they look similar in a file list. Same job as PPT to Word: get the words off the slides. Decks are shared as PPTX when the other person will present, and as PDF when they only need to read. Use DOCX when someone must change the wording, not only read it.
Each slide's text becomes a section in a Word document.
The PPTX file you already have
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.
What a DOCX result is for
The download has to be DOCX, because that is the format the next step named. Use DOCX when someone must change the wording, not only read it. It stores paragraphs, basic headings, and tables well enough for drafts and letters.
The useful result is editable text. Pixel-perfect Word styling is a desktop export.
How to tell that PowerPoint to Word worked
PowerPoint to Word is worth using only when DOCX is what the next step actually named. Same job as PPT to Word: get the words off the slides. What you get from PowerPoint to Word: Each slide's text becomes a section in a Word document. Before you trust it: You do not get a designed handout. For that, use PowerPoint's own handout export. 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. A second pass rarely helps. If the first DOCX file is rejected, read the error from the program that rejected it. Another conversion of a bad result usually makes the file worse, not more compatible. When you are done, you should still have the PPTX original and one DOCX download that you have opened. If those two are the same kind of failure, this was the wrong tool and the page above is the place that says so. Slides are a design. PowerPoint to Word 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 PowerPoint to Word. You start with PPTX and you stop when a real program accepts DOCX. Slide text can be pulled out for a handout or a transcript. A browser conversion into DOCX will not rebuild text boxes, headers, or a magazine layout from a PDF. 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.
You do not get a designed handout. For that, use PowerPoint's own handout export.
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.