Expose a REST API to Watermark Word Documents

How to Add Watermarks to Word Documents via ASP.NET Core REST API

This tutorial guides you on how to expose a REST API for adding watermarks to Word documents in ASP.NET Core. It includes step-by-step instructions, setup details, and deployment guidelines for major platforms.

Steps to Add Watermarks to Word Documents via REST API

  1. Set up an ASP.NET Core Web API project for adding watermarks.
  2. Install Aspose.Words for .NET via NuGet Package Manager.
  3. Create a controller with an endpoint to accept Word files and watermark text or image parameters.
  4. Write code to add text or image watermarks to Word documents.
  5. Test the API locally using tools like Postman or cURL.
  6. Deploy the API on Windows, Linux, or macOS environments.
  7. Configure Nginx or IIS for production deployment.

These steps provide a detailed approach to create and expose the watermark API.

Code Example: REST API for Adding Watermarks

Below is a runnable code snippet for exposing a REST API that adds text watermarks to Word documents:

using System.IO;
using System.Threading.Tasks;
using Aspose.Words;
using Aspose.Words.Drawing;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace WatermarkAPI.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class WatermarkController : ControllerBase
    {
        [HttpPost("add-watermark")]
        public async Task<IActionResult> AddWatermark(IFormFile file, [FromQuery] string watermarkText)
        {
            if (file == null || file.Length == 0 || string.IsNullOrWhiteSpace(watermarkText))
                return BadRequest("Please upload a valid Word document and provide a watermark text.");

            try
            {
                var tempFilePath = Path.GetTempFileName();
                using (var stream = new FileStream(tempFilePath, FileMode.Create))
                {
                    await file.CopyToAsync(stream);
                }

                Document doc = new Document(tempFilePath);
                AddTextWatermark(doc, watermarkText);

                var outputStream = new MemoryStream();
                doc.Save(outputStream, SaveFormat.Docx);

                outputStream.Position = 0;
                return File(outputStream, "application/vnd.openxmlformats-officedocument.wordprocessingml.document", "watermarked.docx");
            }
            catch (System.Exception ex)
            {
                return StatusCode(500, $"Internal server error: {ex.Message}");
            }
        }

        private void AddTextWatermark(Document doc, string text)
        {
            foreach (Section section in doc.Sections)
            {
                var watermark = new Shape(doc, ShapeType.TextPlainText)
                {
                    TextPath = { Text = text, FontFamily = "Arial" },
                    Width = 300,
                    Height = 70,
                    Rotation = -40,
                    FillColor = System.Drawing.Color.LightGray,
                    StrokeColor = System.Drawing.Color.LightGray,
                    WrapType = WrapType.None,
                    BehindText = true,
                    RelativeHorizontalPosition = RelativeHorizontalPosition.Page,
                    RelativeVerticalPosition = RelativeVerticalPosition.Page,
                    Left = 100,
                    Top = 200
                };

                section.HeadersFooters[HeaderFooterType.HeaderPrimary]?.AppendChild(watermark);
            }
        }
    }
}

Deployment on Major Platforms

Windows

  1. Install IIS and configure the site to point to the published application folder.
  2. Publish the application:
    dotnet publish -c Release -o publish

Linux

  1. Install the ASP.NET Core runtime:
    sudo apt-get install -y aspnetcore-runtime-7.0
  2. Publish the application:
    dotnet publish -c Release -o publish
  3. Configure Nginx to proxy traffic to the Kestrel server.

macOS

  1. Install the .NET runtime from the official site.
  2. Publish and run:
    dotnet publish -c Release -o publish
cd publish
dotnet WatermarkAPI.dll

Common Issues and Fixes

  1. Invalid Input Errors: Ensure that the uploaded file is a valid Word document and the watermark text is non-empty.
  2. Access Denied Errors: On Linux/macOS, grant proper permissions to the application folder.
    chmod -R 755 /path/to/app
  3. Performance Issues: For large files, optimize memory usage by processing files directly from disk rather than streams.

This guide has shown you how to create a REST API for adding watermarks to Word documents using Aspose.Words for .NET and deploy it on all major platforms.

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