Add the following dependencies to your Maven configuration:

<dependencies>
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi-ooxml</artifactId>
        <version>5.2.3</version>
    </dependency>
</dependencies>

The following implementation demonstrates creating a structured Word template:

import org.apache.poi.xwpf.usermodel.*;
import java.io.FileOutputStream;
import java.io.IOException;

public class DocumentGenerator {
    
    public void exportToFile(String outputPath) {
        XWPFDocument doc = new XWPFDocument();
        
        XWPFParagraph titlePara = doc.createParagraph();
        titlePara.setAlignment(ParagraphAlignment.CENTER);
        XWPFRun titleRun = titlePara.createRun();
        titleRun.setText("Report Template");
        titleRun.setBold(true);
        titleRun.setFontSize(18);
        
        XWPFParagraph contentPara = doc.createParagraph();
        XWPFRun contentRun = contentPara.createRun();
        contentRun.setText("Dynamic content section");
        
        try (FileOutputStream out = new FileOutputStream(outputPath)) {
            doc.write(out);
        } catch (IOException e) {
            throw new RuntimeException("Document generation error", e);
        } finally {
            try {
                doc.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }
    
    public static void main(String[] args) {
        new DocumentGenerator().exportToFile("output.docx");
    }
}

To variable substitution within exitsing templates, read the source file before processing:

import java.io.FileInputStream;

public void populateTemplate(String templatePath, String targetPath, String replacement) {
    try (XWPFDocument template = new XWPFDocument(new FileInputStream(templatePath));
         FileOutputStream out = new FileOutputStream(targetPath)) {
        
        for (XWPFParagraph paragraph : template.getParagraphs()) {
            for (XWPFRun run : paragraph.getRuns()) {
                String text = run.getText(0);
                if (text != null && text.contains("{{placeholder}}")) {
                    run.setText(text.replace("{{placeholder}}", replacement), 0);
                }
            }
        }
        
        template.write(out);
    } catch (IOException e) {
        throw new UncheckedIOException(e);
    }
}