Are you perhaps referring to Content Stream example?
If yes, note that this example uses a simple Type1 Font (Helvetica) which is one of the Standard 14 Fonts that don’t need to be embedded in a PDF file. But for other fonts, their usage will be more complex.
Nevertheless, I’m afraid that current GemBox.Pdf lacks an easy-to-use API for creating new or editing existing PDF text content.
However, note that we’re actually working on it at this moment, these new planned improvements and API will simplify such tasks.
In the meantime, I would recommend you to try using both GemBox.Pdf and GemBox.Document to accomplish this. For example, please check the AddContent.zip project.
In short, this project uses GemBox.Document to create a new PDF file with the desired content and then uses GemBox.Pdf to append (or prepend) that content to the existing PDF. Using this approach you can add any content that you want (paragraphs, images, tables, hyperlinks, headers, footers, etc.).
As an FYI, for this requirement, you can feel free to use the GemBox.Document Free.
The Free mode enables you to create an unlimited number of documents that have up to 20 paragraphs and thus you can create an unlimited number of new PDF files and append their content to your existing PDF file.