Secure PDF Documents with Digital Signatures in ASP.NET Core Using Syncfusion® .NET PDF Library

A lightweight ASP.NET Core sample that demonstrates how to sign, secure, and validate PDF documents using the Syncfusion .NET PDF Library. The application allows users to apply digital signatures, encrypt PDF files, configure document permissions, and retrieve signature details from signed PDFs.

Pages

Page	Route	Description
Home	/	Landing page with links to both demo pages.
Sign & Secure	/Signature/Sign	Upload (or use the default) PDF, PFX, signature image, then sign + apply encryption/permissions and download.
Validate	/Signature/Validate	Upload (or use the default) signed PDF, view signer certificate and signature info.

Features

• Visible signature image overlay on the last page
• Invisible digital signature (PKCS#7 / CAdES, SHA-256)
• AES-256 encryption with an open password
• Disable printing / copying / editing
• Flatten AcroForm fields
• Read-back of signature + signer certificate details

Project structure

PdfDigitalSignatureAndSecurityDemo
├── Controllers
│   ├── HomeController.cs
│   └── SignatureController.cs
├── Models
│   ├── SignPdfViewModel.cs
│   └── ValidateSignatureViewModel.cs
├── Services
│   ├── PdfSecurityService.cs
│   └── PdfValidationService.cs
├── Views
│   ├── Home
│   │   └── Index.cshtml
│   ├── Signature
│   │   ├── Sign.cshtml
│   │   └── Validate.cshtml
│   └── Shared
│       └── _Layout.cshtml
├── wwwroot
│   └── SampleFiles
│       ├── Input.pdf
│       ├── SignedDocument.pdf
│       ├── Signature.png
│       └── Certificate.pfx
├── Properties
│   └── launchSettings.json
├── Program.cs
├── appsettings.json
└── PdfDigitalSignatureAndSecurityDemo.csproj

Run

cd PdfDigitalSignatureAndSecurityDemo
dotnet restore
dotnet run

Then open https://localhost:5001 (or http://localhost:5000).

Syncfusion license

Set your Syncfusion license key via:

• Environment variable SYNCFUSION_LICENSE_KEY, or
• appsettings.json → Syncfusion:LicenseKey, or
• The SyncfusionLicenseProvider.RegisterLicense(...) call in Program.cs.

A free community license is available at https://www.syncfusion.com/products/communitylicense.

Default sample files

File	Default password (when none supplied in UI)
Certificate.pfx	syncfusion

Replace the bundled Input.pdf, Signature.png, Certificate.pfx, and SignedDocument.pdf with your own files to try the demo end-to-end.