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Sign PDF using C# REST API

Discover how to sign PDF files using the C# REST API in this hands‑on tutorial. You’ll learn to electronically sign a PDF with a C# .NET‑based API by leveraging the Aspose.PDF Cloud SDK. The guide walks you through uploading the target PDF and the signature image to Cloud storage, then applying the signature to the PDF.

Prerequisite

Steps to Sign PDF Online using C# REST Interface

  1. Create a PdfApi instance using your Client ID and Client Secret credentials
  2. Specify the PDF file name, signature file name, and storage folder path
  3. Set the signature’s position and size on the PDF page using Rectangle
  4. Initialize a Signature instance with path, type, password, and visual properties
  5. Populate metadata such as authority, location, contact, and signing date
  6. Upload both the PDF and the certificate file to the configured folder
  7. Call PostSignDocument to apply the digital signature to the uploaded PDF
  8. Retrieve the signed document stream and write it locally as Sample_out.pdf

These steps summarize how to digitally sign PDF using C# REST API. This code connects to Aspose.PDF Cloud, uploads a PDF and a certificate, then digitally signs the document using the provided credentials and signature details. After signing, it downloads the updated PDF and saves it locally as a new file.

Code to Add Signature to PDF using C# RESTful Service

This example illustrates how to sign PDF documents using the C# Low Code API. Keep in mind that the PDF must contain a Signature‑type form field and you must know its exact name—otherwise the API will return an error.

In this guide we’ve walked through signing a PDF using the C# REST API. If you also need to shrink PDF files, explore our tutorial on Compress PDF with C# REST API.

 

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