It is possible that a font which displays fine while editing and outputting using File > Print may not appear at all when using the built-in PDF generation under File > Create PDF.
There are several reasons this may typically happen:
1. All variants of the font are not properly installed.
Fonts are sometimes composed of multiple files, such as separate files for Regular, Bold, Italic, and Bold-Italic. Make sure that, if this is the case, all variants are installed.
Sometimes for whatever reason a font is just not registered/recognized properly when originally installed. In that case, uninstalling and re-installing a font can sometimes fix the issue.
2. The font is not explicitly specified.
Sometimes the application will actually use for display a font different than the one the formatting is currently set to use. This may happen when a character glyph not contained in the current font is used, such as typing Chinese text in a font that does not contain Chinese characters. In that case, the system will try to substitute an appropriate glyph from another font.
If you are going to be using a different/nonstandard font for a section of text, it is important to explicitly specify the font by selecting the text and choosing Format > Format Font (or clicking the Font button in the Formatting panel).
3. The font is not a compatible font file format.
The application's built-in PDF generation may not be able to handle every font type that a particular computer or operating system can. Generally speaking, it can handle fonts of the following formats: TrueType (.ttf and .ttc), OpenType (.otf), and Type 1.
That said, it is not uncommon that a readily available font will not comply entirely with the technical standard, which can lead to difficulty with portability and using the font in some applications. For instance, some True Type Collection (.ttc) fonts on OS X may be incompatible with built-in PDF generation. In those cases, it may be possible to convert the .ttc file into one or more .ttf files.
4. Do not use plain "Courier"
First of all, on Windows, plain "Courier" is a terrible font. Secondly, even on other operating systems, PDF viewers/readers/other programs that open PDFs may substitute their own built-in "Courier" font instead of the one your document is using. This is a known issue with PDF.
If you're still not sure what font to use, please see here.
Finally, you can use a different method of PDF generation.