Hi Beatriz,<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Thank you for considering Aspose.Pdf for .NET.
If your requirement is to merge different small PDF files together into a large PDF file, you may check the following documentation links with details on how to merge the PDF files.
In case your requirement is to add the text to an existing PDF file, the process you are using is fine.To check the issue you are facing, we would request you to please share your template PDF files with us. We will look into it and get back to you soon.
Sorry for the inconvenience,