The platform restricts document and media upload formats – first up Convert your powerpoint to a PDF …
You can then upload as a file. Start a new line and type /file

and either embed it or give the user the option to download it (or open in a new window).
// OR //
Share a Drive link instead

Sharing outside of the organisation can be done, but remember that anyone with the link can see the file.
If the file is confidential, then you need to find a different way to share it, perhaps using Confidential Mode in an email.
If it is cool to make a document public, it is good practice to convert it to universal non-editable format (unless you don’t mend it being reused or altered).
If you are using cloud based storage, designate a public area – a folder, where you can share things without worrying about accidentally sharing too much.
WARNING: If you create any assets inside the public folder those assets inherit the public permissions and could theoretically be found