Embed custom font in PDF file
It appears as though to embed a font in Preview (or at least to ensure that it shows up on an iPad when the iPad does not have the same font installed), you need to perform the following:

Go to File &gt; Print...
Click PDF on the bottom let, and click Save as PDF
Save as a new PDF file

The new PDF file will have the font correctly embedded in it. You may also be able to export as a PDF (again) directly from Preview, although I have not tried this.
The reason that it doesn't get &quot;embedded&quot; upon saving likely has something to do with the text fields staying editable in the PDF. Once you export the PDF, you are unable to edit the text fields any longer in Preview, but the fonts are embedded.