> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/ios/digital-signature/sign-pdf.md).

# Sign a PDF document on iOS

Learn how to digitally sign PDF files with the Apryse SDK, ensuring authenticity and security. Get a full code sample for adding approval signatures to PDF documents using a Digital Certificate. The A

To sign an existing approval signature field in a PDF Document:

{% tabs %}
{% tab title="Obj-C" %}
{% code lineNumbers="true" %}

```objc
PTPDFDoc* doc = [[PTPDFDoc alloc] initWithFilepath: docpath];

// Retrieve the unsigned approval signature field.
PTField* found_approval_field = [doc GetField: approval_field_name];
PTDigitalSignatureField* approval_digsig_field = [[PTDigitalSignatureField alloc] initWithIn_field: found_approval_field];

// (OPTIONAL) Add more information to the signature dictionary.
[approval_digsig_field SetLocation: @"Vancouver, BC"];
[approval_digsig_field SetReason: @"Document approval."];
[approval_digsig_field SetContactInfo: @"www.apryse.com"];

// (OPTIONAL) Add an appearance to the signature field.
PTImage* img = [PTImage CreateWithFile: [doc GetSDFDoc] filename: appearance_img_path encoder_hints: [[PTObj alloc]init]];
PTSignatureWidget* approval_signature_widget = [[PTSignatureWidget alloc] initWithD: [found_approval_field GetSDFObj]];
[approval_signature_widget CreateSignatureAppearance: img];

// Prepare the signature and signature handler for signing.
[approval_digsig_field SignOnNextSave: private_key_file_path in_password: keyfile_password];

// The actual approval signing will be done during the following incremental save operation.
[doc SaveToFile: outpath flags: e_ptincremental];
```

{% endcode %}
{% endtab %}

{% tab title="Swift" %}
{% code lineNumbers="true" %}

```swift
let doc: PTPDFDoc = PTPDFDoc(filepath: in_docpath)

// Retrieve the unsigned approval signature field.
let found_approval_field: PTField = doc.getField(in_approval_field_name)
let found_approval_signature_digsig_field: PTDigitalSignatureField = PTDigitalSignatureField(in_field: found_approval_field)

// (OPTIONAL) Add more information to the signature dictionary.
found_approval_signature_digsig_field.setLocation("Vancouver, BC")
found_approval_signature_digsig_field.setReason("Document certification.")
found_approval_signature_digsig_field.setContactInfo("www.apryse.com")

// (OPTIONAL) Add an appearance to the signature field.
let img: PTImage = PTImage.create(withFile: doc.getSDFDoc(), filename: in_appearance_img_path, encoder_hints: PTObj())
let found_approval_signature_widget: PTSignatureWidget = PTSignatureWidget(d: found_approval_field.getSDFObj())
found_approval_signature_widget.createSignatureAppearance(img)

// Prepare the signature and signature handler for signing.
found_approval_signature_digsig_field.sign(onNextSave: in_private_key_file_path, in_password: in_keyfile_password)

// The actual approval signing will be done during the following incremental save operation.
doc.save(toFile: in_outpath, flags: e_ptincremental.rawValue)
```

{% endcode %}
{% endtab %}
{% endtabs %}

[Digitally sign PDF files](/ios/get-started/samples.md#digitalsignatures) Full code sample which demonstrates using the digital signature API to digitally sign and/or certify PDF documents.

## About Adding An Approval Signature to a PDF Document

The Apryse SDK enables approval signatures in PDF documents using a Digital Certificate, in accordance with the latest PDF specification. By leveraging [public key infrastructure (PKI)](https://en.wikipedia.org/wiki/Public_key_infrastructure) technology, with a certificate issued by a trusted [certificate authority (CA)](https://en.wikipedia.org/wiki/Certificate_authority), a signer can use a certificate-based digital ID to guarantee the authenticity of a signature. Placement of a digital signature using a certificate can also guarantee that a document was not modified since the signature was placed, ensuring the authenticity of the document.

![](https://4149080208-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FgY6xtY9ZQd9XMpvWlGM0%2Fuploads%2Fgit-blob-51c4b698c1ec2efcc0d46686d1342347626f1a9d%2F8130e2be0155c3a56bbf8548f836090a8beb0ac2-299x658.png?alt=media)

Image taken from Apryse WebViewer

Above is an example of a document containing a certified signature, guaranteed by a certificate generated by Apryse.com.


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