The reason you can see the font on your computer is because you have the font installed on your computer. Whereas the person who is viewing the Powerpoint on a different machine, does not have the font installed.
The easiest and most foolproof way to solve this is to change the font you are using in the editable text boxes to a standard one. By a standard font, I mean a font that is already installed on all machines (whether PC, Mac, iPad or otherwise). Here’s a list of fonts that are generally considered safe to work across platforms: Arial, Arial Black, Comic Sans, Courier New, Impact, Georgia, Times New Roman, Trebuchet, Verdana.2) User needs to install the font on their machine
If the person viewing the powerpoint also has the font on their machine, they will have no trouble using it in Powerpoint too. First determine if you anyone can download and install the font. Then you can give your buyers a link to the font.3) Embed the font in Powerpoint
This is the trickiest one to get right. Firstly, you can only embed fonts in Microsoft Powerpoint for Windows. Secondly, you can only embed OpenType and TrueType fonts (how to determine font type). Thirdly, only those fonts that have a embeddable license will actually embed (how to determine embeddable font). You can do this in Microsoft Powerpoint for Windows under File -> Options -> Save. Check Embed fonts in file and embed all characters.
Those are three options. A few TPT sellers who sell editable Powerpoints do the following: create a zip file with the following contents