Document Decryption Tool Using Azure Functions and Syncfusion® Libraries

A serverless Azure Functions application that demonstrates how to decrypt password-protected PDF and Excel documents using the Syncfusion .NET PDF Library and Syncfusion XlsIO Library. The application provides a modern web interface for uploading encrypted documents, entering passwords, and downloading decrypted files securely.

Pages

Page	Route	Description
Document Decryption Tool	/api/Ui	Upload password-protected PDF or Excel documents, provide the password, and download the decrypted file.
Document Decryption API	/api/DecryptDocument	Backend API endpoint that processes uploaded PDF and Excel files and returns the decrypted document.

Features

• Decrypt password-protected PDF documents
• Decrypt password-protected Excel workbooks (.xlsx, .xls)
• Browser-based drag-and-drop file upload
• Secure server-side document processing
• Password input with visibility toggle
• Automatic download of decrypted documents
• Supports PDF and Excel file validation before processing
• Clear error reporting for invalid passwords and unsupported file types
• Azure Functions isolated worker (.NET 8) architecture

Supported File Types

File Type	Extension
PDF Document	.pdf
Excel Workbook	.xlsx
Excel Workbook (Legacy)	.xls

Project Structure

DocumentDecryptionFunction
├── Functions
│   ├── Function1.cs
│   └── UiFunction.cs
├── wwwroot
│   ├── index.html
│   ├── styles.css
│   └── script.js
├── Properties
│   └── launchSettings.json
├── Program.cs
├── host.json
├── local.settings.json
└── DocumentDecryptionFunction.csproj

How It Works

PDF Decryption

The application uses the Syncfusion PDF Library to:

• Open encrypted PDF documents
• Validate the provided password
• Remove user and owner passwords
• Save and return the decrypted PDF document

Excel Decryption

The application uses Syncfusion XlsIO to:

• Open encrypted Excel workbooks
• Validate the provided password
• Remove workbook open-password protection
• Save and return the decrypted workbook

Run

cd DocumentDecryptionFunction
dotnet restore
dotnet build
func start

Alternatively:

dotnet run

Open the application in your browser:

http://localhost:7154/dotnet-document-decryption-azure-functions/

## Required NuGet Packages

```xml
<PackageReference Include="Syncfusion.Pdf.Net.Core" Version="34.2.8" />
<PackageReference Include="Syncfusion.XlsIO.Net.Core" Version="34.2.8" />
<PackageReference Include="Microsoft.Azure.Functions.Worker" Version="2.52.0" />
<PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore" Version="2.1.0" />

Syncfusion License

Register your Syncfusion license using one of the following methods:

• Environment variable: SYNCFUSION_LICENSE_KEY
• Azure Application Settings
• Program.cs using:

Syncfusion.Licensing.SyncfusionLicenseProvider.RegisterLicense(
    "YOUR LICENSE KEY");

A free community license is available at:License

Sample Request

The application accepts a multipart/form-data request containing:

file       - PDF or Excel document
password   - Document password

Security Notes

• Documents are processed in memory.
• Uploaded files are not permanently stored.
• Passwords are used only during document processing.
• Decrypted files are returned directly to the client for download.

Technology Stack

• .NET 8
• Azure Functions v4 (Isolated Worker)
• Syncfusion PDF Library
• Syncfusion XlsIO
• HTML, CSS, JavaScript
• OpenTelemetry
• Application Insights

Use Cases

• Remove password protection from PDF files
• Remove workbook passwords from Excel files
• Document migration and archival workflows
• Secure document processing in cloud environments
• Integration with enterprise document management systems