Watermarks play a crucial role in professional document management — from brand identity to content protection. In Excel workbooks, they can mark a sheet as “Confidential”, “Draft”, or include a company logo for consistent branding. This article provides the necessary details about our cloud-based SDK providing flexibility, automation, and precision for inserting watermark in Excel workbook.

Excel Processing API

Aspose.Cells Cloud SDK for .NET offers C# developers an advanced, scalable, and secure way to manage Excel files online. When it comes to watermarking, it provides:

  • Cloud-based automation – Add or remove watermarks without local installations.
  • Cross-platform support – Works across .NET Core, .NET Framework, and serverless environments.
  • High performance – Efficiently processes large workbooks in the cloud.
  • RESTful integration – Simplifies integration using SDKs or direct HTTP requests.

Whether you need to apply a watermark to Excel worksheets for protection or branding, Aspose.Cells Cloud makes the process effortless.

Environment Setup

Before you begin with Excel Workbook processing, make sure you have:

  1. A valid Aspose.Cloud account (to obtain Client ID and Secret).
  2. Installed Visual Studio or any .NET-compatible IDE.
  3. An Excel workbook (XLS or XLSX) and an image file (logo or watermark).

Install the SDK using NuGet Package Manager:

Install-Package Aspose.Cells-Cloud

Watermark Excel using C#

The following example demonstrates how to upload an Excel workbook to cloud storage and apply a watermark image using Aspose.Cells Cloud SDK for .NET.

  1. Create an instance of CellsApi where we pass client credentials as arguments.
CellsApi cellsInstance = new CellsApi(clientID, clientSecret);
  1. Upload the Excel workbook to cloud storage.
cellsInstance.UploadFile(input_Excel, File.OpenRead(input_Excel));
  1. Convert image stream to byte array.
byte[] imageBytes = File.ReadAllBytes(watermarkImage);
  1. Call the API to apply the watermark image as a background to all worksheets in the workbook.
var response = cellsInstance.CellsWorkbookPutWorkbookBackground(input_Excel, imageBytes, null);

Insert Watermark in Excel using cURL

If you prefer command-line or script-based automation, Aspose.Cells Cloud also supports RESTful cURL operations.

Step 1. - Create an ACCESS_TOKEN based on client credentials:

curl -v "https://api.aspose.cloud/connect/token" \
-X POST \
-d "grant_type=client_credentials&client_id=XXXXXX-XXXXXX-XXXXXX&client_secret=XXXXXXXXXXXXX" \
-H "Content-Type: application/x-www-form-urlencoded" \
-H "Accept: application/json"

Step 2- Upload an Excel File to the Cloud Storage.

curl -v "https://api.aspose.cloud/v3.0/cells/storage/file/{filePath}" \
-X PUT \
-F file=@{localFilePath} \
-H "Content-Type: multipart/form-data" \
-H "Authorization: Bearer {ACCESS_TOKEN}"

Step 3 - Add Watermark Image to Excel workbook.

curl -v "https://api.aspose.cloud/v3.0/cells/{excelFile}/background" \
-X PUT \
-H  "accept: multipart/form-data" \
-H  "authorization: Bearer {ACCESS_TOKEN}" \
-H  "Content-Type: multipart/form-data" \
-d  "File":{"watermarkImage"}

Replace:

  • {excelFile} - name of input Excel file in cloud storage.
  • {ACCESS_TOKEN} - JWT token generated above.
  • {watermarkImage} - Image file to be used as watermark.

Watermark Excel Online

Want to test the feature without coding?

Try our Free Online Excel Watermark App — powered by Aspose.Cells Cloud. Simply upload your Excel workbook, apply your logo or watermark image, and download the resultant file instantly.

watermark excel online

Conclusion

Whether you’re developing a document automation system or integrating Excel file branding into your application workflow, this SDK enables seamless Excel watermarking in the cloud—secure, scalable, and developer-friendly.

Frequently Asked Questions (FAQs)

  1. Does the Excel watermark API support both image and text watermarks? The API allows you to add image-based watermarks (such as PNG, JPEG, or BMP). Concerning Text-based watermarks, you can implement it by overlaying text via the drawing or shape APIs.

  2. Can I apply a different watermark to each worksheet in the Excel file? Yes. The Aspose.Cells Cloud SDK provides granular control over individual worksheets. You can use the CellsWorksheetPutBackground() method to apply a unique watermark to a specific worksheet rather than the entire workbook.

  3. Do I need Microsoft Excel installed to use the Aspose.Cells Cloud SDK? No. The Aspose.Cells Cloud SDK for .NET is entirely cloud-based, meaning you can apply or remove watermarks from Excel files without installing Microsoft Excel or any additional desktop software.

  4. Is my data secure during Excel watermark processing in the cloud? Yes. Aspose.Cells Cloud uses SSL encryption for data transmission and stores files securely in the cloud. Uploaded files are automatically deleted after the operation is completed (based on retention period you select for your mapped storage).

We recommend you visit the g links to learn more about: