Thank you for considering Aspose. The main difference between Aspose.Words and Aspose.Editor is that Aspose.Words is a non-visual Word processing component while Aspose.Editor is a visual Word document editing component (control) intended to be used in WinForms applications. Here are the pages that would help you to compare the functionality of the products:
Peforming mail merge is one of the primary usage scenarios of Aspose.Words. It provides rich document processing capabilities such as opening DOC and HTML documents, processing, and saving the documents to a number of formats such as DOC, HTML, PDF (in conjunction with Aspose.Pdf), RTF, WordML (the last two are available in new Aspose.Words 4.0 which is currently beta but will get to final version this week).
You can download an evaluation version of Aspose.Words or Aspose.Editor for free:
Feel free to post your further questions here!