#!c#

//Will not deal with mergefields nested in other fields (IF, for example)
    private void btnGetMergeFields_Click(object sender, EventArgs e)
    {
        string fileName = @"C:\test\MergeFields.docx";
        using (WordprocessingDocument pkgDoc = WordprocessingDocument.Open(fileName, true))
        {
            string fieldList = string.Empty;
            Document doc = pkgDoc.MainDocumentPart.Document;
            //Get all field code elements in the document
            IEnumerable<FieldChar> fldChars = doc.Descendants<FieldChar>();
            if (fldChars == null) return; //No field codes in the document

            // bool fldStart = false;
            FieldChar fldCharStart = null;
            FieldChar fldCharEnd = null;
            FieldChar fldCharSep = null;
            FieldCode fldCode = null;
            string fldContent = String.Empty;
            foreach (FieldChar fldChar in fldChars)
            {
                string fldCharPart = fldChar.FieldCharType.ToString();
                switch (fldCharPart)
                {
                    case "begin": //start of the field
                        fldCharStart = fldChar;
                        //get the field code, which will be an instrText element
                        // either as sibling or as a child of the parent sibling
                        fldCode = fldCharStart.Parent.Descendants<FieldCode>().FirstOrDefault();
                        if (fldCode == null) //complex field
                        {
                            fldCode = fldCharStart.Parent.NextSibling<Run>().Descendants<FieldCode>().FirstOrDefault();
                        }
                        if (fldCode != null && fldCode.InnerText.Contains("MERGEFIELD"))
                        {
                            fldContent = fldCode.InnerText;
                            fieldList += fldContent + "\n";
                        }
                        break;
                    case "end": // end of the field
                        fldCharEnd = fldChar;
                        break;
                    case "separate": //complex field with text result
                        //we want to put the database content in this text run
                        //yet still remove the field code
                        //If there's no "separate" field char for the current field,
                        //we need to insert it somewhere else
                        fldCharSep = fldChar;
                        break;
                    default:
                        break;
                }
                if ((fldCharStart != null) && (fldCharEnd != null)) //start and end field codes have been found
                {
                    if (fldCharSep != null)
                    {
                        DocumentFormat.OpenXml.Wordprocessing.Text elemText = (DocumentFormat.OpenXml.Wordprocessing.Text)fldCharSep.Parent.NextSibling().Descendants<DocumentFormat.OpenXml.Wordprocessing.Text>().FirstOrDefault();
                        elemText.Text = fldContent;
                        //Delete all the field chars with their runs
                        DeleteFieldChar(fldCharStart);
                        DeleteFieldChar(fldCharEnd);
                        DeleteFieldChar(fldCharSep);
                        fldCode.Remove();
                    }
                    else
                    {
                        DocumentFormat.OpenXml.Wordprocessing.Text elemText = new DocumentFormat.OpenXml.Wordprocessing.Text(fldContent);
                        fldCode.Parent.Append(elemText);
                        fldCode.Remove();
                        //Delete all the field chars with their runs
                        DeleteFieldChar(fldCharStart);
                        DeleteFieldChar(fldCharEnd);
                        DeleteFieldChar(fldCharSep);
                    }
                    fldCharStart = null;
                    fldCharEnd = null;
                    fldCharSep = null;
                    fldCode = null;
                    fldContent = string.Empty;
                }

            }
            this.txtMessages.Text = fieldList;
        }
    }
    private void DeleteFieldChar(OpenXmlElement fldCharStart)
    {
        Run fldRun = (Run) fldCharStart.Parent;
        fldRun.RemoveAllChildren();
        fldRun.Remove();
    }
    }

#!c#

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Aspose.Words;

namespace MailMerge
{
    class Program
    {
        static void Main(string[] args)
        {
            string projectFiles = Path.GetFullPath("../../Files/");

            Document doc = new Document(projectFiles + "Template.docx");

            // Fill the fields in the document with user data.
            doc.MailMerge.Execute(
                new string[] { "FullName", "Company", "Address", "Address2", "City" },
                new object[] { "James Bond", "MI5 Headquarters", "Milbank", "", "London" });

            // Saves the document to disk.
            doc.Save(projectFiles + "MailMerge Result Out.docx");

            System.Console.WriteLine("Press any key to continue.");
            System.Console.ReadKey();
        }
    }
}