Hey, Alexandre,The RadFixedDocument is a type, used by the RadPdfProcessing library to represent and work with PDF files, while the RadFlowDocument is the equivalent type for the RadWordsProcessing library and is used to work with .docx files.
The RadWordsProcessing library supports more formats than RadPdfProcessing and is essentially the middle piece when converting HTML to PDF. The original HTML file or string is parsed using the HtmlFormatProvider and imported into a RadFlowDocument, which is then exported to a PDF file using the PdfFormatProvider. I've attached a small .NET Framework project, which does this for your ease.
To do this, the project makes use of several assemblies listed in our RadWordsProcessing: Getting Started article:
Note that the last library is only used to export a RadFlowDocument to PDF. If you need to manipulate a PDF file it is better to try the RadPdfProcessing library, which uses different assemblies. Here is a great place to start with it - RadPdfProcessing: Getting Started.
I hope this is useful to you. Please let me know if I can further help.