We have an application (a custom network management tool for building automation) that supports printing labels that you can cut out and insert into the devices' front displays. In earlier versions of the tool (not developed in my company), the application just pushed the strings into an Excel file that the field technician could then manipulate (like formatting text). We didn't do this in the new version because it was hard (impossible) to keep the Excel file in sync, and to avoid a binding to an external application (let alone different versions of Excel).

We're using PDFSharp for rendering the labels. It has a System.Drawing-like interface, but can output to a System.Drawing.Graphics (screen / printer) as well as to a PDF file, which is a requirement.

Later, basic formatting was introduced like Font Family, Style, Size, Color which would apply to one label (i.e. to exactly one string). Now the customer wants to be able to apply these formats to single characters in a string. I think the easiest way would be to support a subset of RichText. It's not as easy as I thought though.

Currently the editor just displays a TextBox for the label you want to edit, with the font set to the label's font. I thought I'd just replace it with RichTextBox, and update the formatting buttons to use the RichTextBox formatting properties. Fairly easy. However, I need to draw the text. I know you can get the RichTextBox to draw to a HDC or System.Drawing.Graphics - but as already said, I need it to use PDFSharp. Rendering to bitmaps is not an option, since the PDF must not be huge, and it's a lot of labels. Unfortunately I couldn't get the RichTextBox to tell me the layout of the text - I'm fine with doing the actual rendering by hand, as long as I know where to draw what. This is the first question: How can I get the properly layouted metrics of the rich text out of a RichTextBox? Or is there any way to convert the rich text to a vector graphics format that can be easily drawn manually?

I know about NRTFTree which can be used to parse and manipulate RichText. The documentation is bad (actually I don't know, it's Spanish), but I think I can get it to work. As far as I understood, it won't provide layouting as well. Because of this, I think I'll have to write a custom edit control (remember, it's basically just one or two line labels with basic RTF formatting, not a full-fledged edit control - more like editing a textbox in PowerPoint) and write custom text layout logic that used PDFSharp rather than System.Drawing for drawing. Is there any existing, even if partial, solution available, either for the editing or for doing the layout manually (or both)?

Or is there an entirely different approach I'm just not seeing? Bonus points if exporting the label texts as RTF into a CSV file, and then importing in Excel retains the formatting.

For the editing part, I need it to work in Windows Forms. Other than that it's not Windows-Forms-related, I think.