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.NET SDK

eSignature SDK for .NET and C# applications

Send documents for signature from your C# code with the BoldSign .NET SDK. Signers sign in their browser from an email link, or inside your app.

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  • Install from NuGet
  • API key or OAuth 2.0
Your CompanyPreviewSend
Assignee
David
SERVICE AGREEMENT
Company signatureSign here*
Client signatureSign here*
AgreementsController.cs.NET SDK
var documentClient = new DocumentClient(apiClient);var signer = new DocumentSigner( name: "David", emailAddress: "david@cubeflakes.com",var request = new EmbeddedDocumentRequest(){ Title = "Service Agreement", Signers = new List<DocumentSigner> { signer }, SendViewOption = PageViewOption.PreparePage, ShowToolbar = true};var embeddedSendCreated =  documentClient.
    CreateEmbeddedRequestUrl(request);var sendUrl = embeddedSendCreated.SendUrl;
Sample .NET web app at yourapp.example with BoldSign embedded: the prepare page of a service agreement assigned to David, with Preview and Send buttons, beside the C# code from BoldSign’s .NET SDK docs that creates this embedded request

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The problem

Why is adding eSignatures to a .NET app harder than it looks?

Signing is quick. Legal validity, identity checks, reminders, an audit trail, and a sealed PDF are not. With the BoldSign .NET SDK, you get all five from your C# code.

  • The signature is the easy part

    Capturing a drawn or typed signature takes a day. The record around it takes months.

  • The record has to hold up

    A sealed PDF needs a trusted certificate that you buy, store, and renew. Every action needs a timestamp.

  • You own every fix

    Reminders, status tracking, and storage are all code your team writes, runs, and patches.

The solution

How can you add eSignatures to a .NET app without building them?

The BoldSign .NET SDK gives your C# code two routes to a signature. BoldSign runs the signing behind both. Your app creates the document, names the signers, and tracks what comes back.

  • Send for signature from your code

    Your app passes the document and signers to BoldSign, and each signer gets their own email link.

  • Embed signing in your product

    BoldSign returns a signing URL you drop into your own page. The signer signs the document inside your app, without leaving it.

Capabilities

What can your C# app do with the .NET eSignature SDK?

With the BoldSign .NET SDK, your C# app handles the whole signing flow. Every completed PDF is digitally signed.

  • Send documents for signature

    Send a contract or form to one signer or several, in the order you set.

    See the eSignature API

  • Sign inside your app

    Show the signing page in your own .NET pages, so the signer never leaves your product.

    See embedded signing

  • Prepare and send in your app

    Your users drag fields onto the PDF and send it, all inside your .NET app.

    See embedded sending

  • Send from templates

    Store a reusable template once, then send it to new signers from C#.

    See templates

  • Check who is signing

    Set a check per signer: access code, email code, SMS code, KBA, or ID verification.

    See signer authentication

  • Know when it is signed

    Receive each status change on your webhook endpoint, then pull the signed PDF and audit trail.

    See webhooks

Works in: server-side .NET apps on Windows, Linux, and macOS. Keep the SDK on your server, since it carries your API key.

Get started

How do you start sending from a .NET app?

You send from a .NET app with the BoldSign .NET SDK in 3 steps: install, authenticate, and send.

  1. Install from NuGet

    dotnet add package BoldSign.Api

    Runs on .NET Framework 4.5.2 or later, and on .NET 5 or later.

  2. API authentication

    var apiClient = new ApiClient("https://api.boldsign.com", "Your-API-Key-Here");

    Connect your API key, or use an OAuth 2.0 token.

  3. Send the document

    documentClient.SendDocument(...);

    The result holds the document ID.

Using an AI coding tool? Connect BoldSign’s coding assistant (MCP), then try this prompt. Set up the coding assistant.Add a button to my ASP.NET Core app that sends a document with the BoldSign .NET SDK.

See the full C# walkthrough
Why BoldSign

Why choose BoldSign for .NET developers

BoldSign suits .NET teams that want signing in their product without building or maintaining it.

  • One package for the whole flow

    Sending, embedded signing, templates, and signer identity checks all come from the BoldSign .NET SDK.

  • Write .NET code with your AI coding tool

    BoldSign’s coding assistant (MCP) plugs into VS Code, Cursor, or Claude. It answers SDK questions from BoldSign’s docs, with no API key.

  • Build it all before you pay

    Build and test the whole flow in a free sandbox, then change the key at go-live.

  • Signers need no account

    Nobody who signs needs a BoldSign account or an app download.

  • Legally binding signatures

    Signatures you collect with BoldSign are legally binding under the ESIGN Act, UETA, and eIDAS.

Security

How are documents sent from your code kept secure?

BoldSign encrypts every document twice with AES-256. Its security controls are independently audited for SOC 2 Type 2. Your account’s Compliance page lists each standard BoldSign meets, shown below.

Compliance

BoldSign meets global security and compliance standards to protect your documents and data. Manage the settings below to align with your organization’s requirements.

US flag

Data Residency

Active (US - Global)

Your documents and signer data are securely stored in your selected region to meet data sovereignty and local regulatory requirements.

View Data Residency Policy
HIPAA logo

HIPAA Compliance

Enabled

Enable HIPAA mode to protect PHI using administrative, technical, and physical safeguards aligned with HIPAA regulations.

View Details
PCI DSS logo

PCI DSS

Compliant

Payments are securely processed through Stripe, a PCI DSS Level 1-certified provider, ensuring the safe handling and encryption of all payment data.

View PCI DSS Policy
CCPA logo

CCPA & CPRA

Compliant

Ensures compliance with California privacy laws, giving residents transparency and control over their personal data, including rights to access, delete, and opt out.

View Privacy Policy
AICPA SOC logo

SOC 2 Type II

Compliant

BoldSign has successfully completed a SOC 2 Type II audit, validating our controls for security, availability, confidentiality, and data integrity.

Request SOC 2
US flag

UETA & ESIGN

Compliant

BoldSign ensures that all e-signatures are legally binding and compliant with the U.S. ESIGN Act and the Uniform Electronic Transactions Act (UETA).

View UETA & ESIGN Policy
EU flag

eIDAS (SES)

Compliant

BoldSign complies with the EU eIDAS Regulation (910/2014) and supports Simple Electronic Signatures (SES) by default.

View SES Policy
EU flag

eIDAS (QES)

Enabled

Enable Qualified Electronic Signatures (QES) for contracts requiring the highest legal assurance under eIDAS.

View QES Policy
The compliance panel in your BoldSign account.
For IT and procurement

Security and procurement documents for eSignature

IT and procurement teams can read BoldSign’s security policy, data processing agreement, and subprocessor list online. They can also request the SOC 2 Type 2 report.

What it costs

Limits and costs to know before you send from .NET with BoldSign

The BoldSign .NET SDK is free to install from NuGet. Live documents run on a BoldSign API plan. Prices are in USD.

  • $30 Enterprise API plan, per month 40 envelopes included, then $0.75 each.
See all limits and add-on prices
Good to know
  • 2,000 API requests an hour per account The sandbox allows 50 an hour.
Related

More guides for building eSignatures in .NET

  • Page

    All eSignature SDKs

    Compare the five official BoldSign SDKs.

    See all SDKs
  • Page

    Embedded signing

    Open the signing page inside your own app.

    See embedded signing
  • Guide

    ASP.NET Core example

    Add BoldSign signing to an ASP.NET Core project.

    Read the guide
  • Guide

    Build an AI agent

    Let an AI agent send documents through the BoldSign MCP server.

    Read the guide
Common questions

Questions about the .NET eSignature SDK

Is there a .NET digital signature SDK?

Yes. The BoldSign .NET SDK, published on NuGet as BoldSign.Api, is BoldSign’s official SDK for .NET and C#. People sign electronically, and BoldSign seals each completed PDF with an AATL certificate.

Can I add eSignatures to an ASP.NET Core app?

Yes. The BoldSign .NET SDK installs in ASP.NET Core like any NuGet package. The ASP.NET Core guide walks through a full example.

How do webhooks work with the .NET SDK?

Webhooks are set up once in your BoldSign account, under API then Webhooks, not in the SDK. BoldSign posts each status change to your HTTPS endpoint, so your .NET app never polls for status. Set up a webhook.

Does the .NET SDK support OAuth 2.0?

Yes. Pass a bearer token to the SDK’s configuration instead of an API key. See OAuth 2.0 setup.

How do I use the Europe, Canada, or Australia region?

Pass your region’s base URL when you create the API client, such as api-eu.boldsign.com for Europe. US accounts need no change. See all base URLs.

Can I test the .NET SDK for free?

Yes. Create a free BoldSign API sandbox, then use its API key with the .NET SDK. Sandbox documents are for testing only.

Get started

Send your first document from C#

Open a free BoldSign API sandbox, install the .NET SDK from NuGet, and send your first document.

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  • 30-day free trial
  • No credit card required

Last updated: October 18, 2026