import com.spire.doc.Document;
import com.spire.doc.FileFormat;
import com.spire.doc.documents.TextSelection;

import java.awt.*;


public class FindHighlightDemo {
    public void findHeighlight(String docFile, String findText, String resultFilePath){
        Document doc = new Document();
        doc.loadFromFile(docFile);
        TextSelection[] textSelections = doc.findAllString(findText, false, true);
		if(textSelections!=null){
			for (TextSelection selection : textSelections) {
				selection.getAsOneRange().getCharacterFormat().setHighlightColor(Color.YELLOW);
			}
		}
        doc.saveToFile(resultFilePath, FileFormat.Docx);
    }
}

using System;
using System.Drawing;
using Spire.Doc;
using Spire.Doc.Documents;
using Spire.Doc.Fields;

namespace DemoOnlineCode
{
    class FindAndHighlight
    {
        public void demoFindAndHighlight(String docFile, String searchText)
        {
            Document document = new Document(docFile, FileFormat.Auto);

            TextSelection[] textSelections
                = document.FindAllString(searchText, false, false);
            if (textSelections != null)
            {
                foreach (TextSelection selection in textSelections)
                {
                    TextRange textMatched = selection.GetAsOneRange();
                    textMatched.CharacterFormat.HighlightColor = Color.Yellow;
                }
            }

            document.SaveToFile("demo.docx", FileFormat.Docx);
        }
    }
}