Two main choices
1) Embed the font in the PDF.
2) Render/export the file as an image.

The former may see you need a better program for it, and the latter will obviously make any editing or copy pasting for those with the PDF more annoying. Equally for the former I am not sure if every device, much less every security setting, will respect that. Depending upon how the custom font is made it may be able to be substituted too so it is at least readable -- fancy versions of existing characters using the same encoding that it will normally use vs something entirely new or custom.

Most means of embedding a font seem to be the program making it related (embed PDF fonts with indesign, ms word... being choice searches) and I am not entirely sure how well the PDF printers handle such things.

Personally I got a bit broken by embedded/downloaded fonts in the internet explorer days so I am wary to this day about that sort of thing -- I don't even like doing it in CSS now it is all fairly safe. If I have to then I might render whatever section as an image and put that in instead, though for 90% of what I do it is a graphic header or fancy table or something so that is not so bad.

 

You can actually take the font, stick it in the PDF and the reader will hopefully take the font back out and for just that document render it accordingly. It is a fairly new addition to PDF and not all readers might support it for whatever reason (ever suffered a phone's PDF reader? Or the one a browser might include?), however the big ones like adobe's own, foxit and whatever else of similar calibre the kids are using this week should have the option to do it (some security settings may block it for whatever reason).

The alternative is to render the custom font using thing as a picture and do a insert picture in whatever editor you are using. As it is just a picture it will not have to render any text and it will display it as a picture. Being a picture then nobody can easily select text to copy-paste, use a reader program for the hard of sight, blow up the image to any size they like, the file will probably be bigger, while bigger it may also be worse quality if the PDF export reduces image quality and all else that such a thing leads to. If you are struggling to visualise it then I am sure you have at some point downloaded a book/document someone scanned in, saved as a bunch of pictures and then exported it all in a PDF; you would be doing a version of this.

When you say create a font do you mean like a normal font for normal language? That differs slightly, at least as far as boxes/unicode numbers appearing, from creating a font for an ancient script which unicode does not support, or a script that is totally custom (I read a lot of trashy fantasy books, occasionally one will create some magic scribbles and try to have that in the final book).
For a normal language ( https://unicode-table.com/en/ ) then the PDF reader will hopefully still display the proper character. Your sizing, spacing, kerning and whatever else you might have done will probably be broken/pointless but it should display readable text still.

On photoshop I am never quite sure what it does any more -- despite not being the best idea various people used it to make websites and after a while the people coding it started to play to it, this has trickled into other things.

"late response"
It was three hours and it is not like I had an expectation of anything, you had not promised to get me something or otherwise do something.

 

While you can still make bitmap fonts most fonts since... probably windows 3.1 have been vector image based and most things rely on this concept -- I likely need not tell you about the perils of scaling images. A black on white (or similar contrast) image is reasonably well suited for conversion/tracing but be aware that font making it a field of art unto itself ( http://blog.extensis.com/fonts/theres-always-a-cost-for-free-fonts-the-risks-of-using-free-fonts.php ).

Also just in case you were not aware that are a billion decorative and non standard fonts in places like https://www.fontsquirrel.com/ , many of which are free even for commercial use.