Digital Signatures are a type of Electronic Signature that uses a certificate-based Digital ID obtained from a cloud-based trust service provider or the signer's local system.

A digital signature identifies the person signing a document like a conventional handwritten signature. Unlike a handwritten signature, a certificate-based signature is difficult to forge because it contains encrypted information unique to the signer. It can be easily verified and informs recipients whether the document was modified after the signer initially signed it.

Adobe Acrobat Sign supports digital signatures by simply placing the Digital Signature field on a form (either via Text Tags, drag and drop in the Acrobat Sign Authoring environment, or authoring in Adobe Acrobat with Acroforms).

Availability:

Digital signatures are available for Acrobat Standard, Acrobat Pro, and Acrobat Sign Solutions license plans.

Configuration scope:

Digital signatures can be enabled at the account and group levels.

Digital signatures can be applied in two ways through the Acrobat Sign service:

Digital Signature Time Stamps

When applying digital signatures, time stamps are a critical component of both the US and EU signature compliance standards.

The time stamp acts as a locking mechanism for both the signer’s identity and the document itself. Identity can be established in several ways (certificate, logon, ID card, etc.), but the time stamp has to be provided by a trusted and authorized time-stamping authority (TSA).

The time stamp guarantees the Long-Term Validity (LTV) of the signed agreement by locking the signature as well as the document, essentially providing a lock for the lock. This is critical for digital signature compliance because personal signing certificates can expire, while the time stamp LTV can be renewed over time without changing the validity of the signature. The LTV time stamp assures the certificate was valid when applied and extends the validity of the signed agreement beyond the time scope of the signer’s actual certificate.

Note:

The Time Stamp evidence is displayed in the digital signature appearance using the ISO 8601 notation.

Qualified Timestamp for e-IDAS compliance in the European Union

All accounts on the Acrobat Sign EU1 instance in Europe have e-IDAS-compliant Qualified Timestamps applied by default. (Know what instance you are on)

How it's used

For Senders

From the sender's perspective, all that is required is for a Digital Signature field to be placed on the document that is being sent for signature.

Note:

Digital Signatures occupy a bigger footprint on the page due to the additional content in the signature. Keep this in mind when designing your document signature fields.

The drag-and-drop authoring environment showing both the electronic signature field and the digital signature field.

For Document/Template Authors

When a recipient applies a cloud-based signature, they can place up to 10 digital signatures. All digital signature fields beyond the first 10 are converted to the standard e-signature field type.

If the recipient is expected to sign the document by downloading the file and applying their own digital signature certificate using Acrobat, only one digital signature field is allowed on the agreement. If a document contains multiple digital signature fields, the recipient isn't presented with the option to download and apply a local signature.

Keep in mind that just because one signer is using a digital signature, that does not mean that any other signers are required to. It's perfectly valid to have only your internal signers apply digital signatures while external signers use the e-signature field type (or vice versa).

Note:

When multiple signatures are applied for one recipient, each field should have a unique name. e.g., digsig1_:signer1: digitalsignature, digsig2_:signer1: digitalsignature, and so on.

If a digital signature text tag name is duplicated, Acrobat Sign automatically renames the fields by adding a "-n" appendix, where 'n' is a number starting from 1 and is incremented for each duplicated field name found. e.g., will become digsig1-1_es_:signer1:digitalsignature and digsig1-2_es_:signer1:digitalsignature and so on.

Using Drag and Drop Authoring

Template creators will find the Digital Signature field in the Signature Fields section of the Authoring environment.

Below you can see the e-signature field on the left, and the digital signature field on the right.

Text Tag Syntax

The syntax for a digital signature field uses the argument :digitalsignature

e.g, digsig1_es_:signer1:digitalsignature

Building forms in Acrobat

Like all other field types, you can replicate the functionality of a Text Tag when building your documents in Acrobat by renaming the field to contain the full text tag with all arguments (but not the brace pairs on either end).

The Signer's experience

Because digital signatures are certificate-based, signers must obtain a Digital ID before applying their signature. This Digital ID can be obtained from one of several cloud signature providers or by applying the signature using Adobe Acrobat or Acrobat Reader, using a local Digital ID.

The Acrobat Sign solution walks the Signer through the process:

Open the agreement and fill in any required fields
Choose from existing Digital IDs or create a new one
Apply the signature

Once the signature is applied, the signature cycle continues as usual.

Open the agreement and fill in the fields...

Signers are notified via email, and instructed to open the agreement by clicking the Review and sign button
Once the document is open, the signer can read the document and fill in any fields that are needed. All required fields need to be completed before the signer can advance the signature process.

Mousing over the digital signature field prompts a text balloon with additional instructions.
Clicking into the field opens an overlay asking the signer to select one of two paths:
- Cloud Signature
- Download and Sign With Acrobat
Select Cloud Signature, and then select Next.
A new overlay is presented, asking the signer to select an identity provider from a drop-down.
- Only providers listed in the drop-down can be used
- Signers that do not have a permissible Digital ID can click the Click to get a new Digital ID link, and be routed to obtain a new Digital ID from one of several cloud signature providers.
- Once they have established a new Digital ID, they can return to the signature process.
The identity provider challenges the signer to authenticate to their service
Once successfully authenticated, the signer is presented with a list of valid Digital IDs to choose from.
- Select the Digital ID
- Click Next
A preview of the signature is presented.
- Click Edit Signature to:
  
  Manually sign via mouse or touch pad
  
  Upload a signature image
- Click OK when ready to proceed
The signer is returned to the agreement and prompted to Click to Sign
The identity provider then may require an additional, second-factor authentication.

eg: The below provider requires a static PIN, established when setting up the Digital ID, and a one-time password.
- Enter any required values, and click OK
When the second-factor authentication is successfully entered, the document is signed, and a success message is displayed.

Configuration

To review and edit the feature controls:

Log in as an administrator and navigate to your Account Settings menu.
Select the Digital Signatures tab.

The full Digital Signature page in the Admin configuration menu

The configurable options are:

Enable signers to import their digital signature from one or more sources:

Download and Sign With Acrobat - Allows the signer to use a self-certified signature.
- If you have a requirement for a digital signature in your process, check with your legal team to ensure a self-signed certificate is acceptable before enabling this option.
Cloud Signatures - Enables the option to use a cloud-based digital signatures for your signers, which makes digital signing also possible on mobile devices
- If digital signatures are important to your signing process, enabling the cloud-based option is strongly recommended.

The Digital Signature configuration page with the Download and Cloud singature options highlighted.

When Cloud Signatures are enabled, The list of signature providers is activated on the page. One or more providers must be selected, and the selected vendors are the only options from which the signer may choose.

If there is a vendor that your company prefers that signers use, then the Preferred Cloud Signature Provider options will select that vendor automatically when the recipient is prompted to sign. The recipient still has the option to select a different vendor from the list you have allowed.

The Digital Signature configuration page with the Allowed and Preferred signature provider options highlighted.

The option to send the agreement information back to your Cloud Signature Provider allows the signature provider to associate your agreements with the consumption of the signatures that your company has purchased.

Customers who want to have a detailed understanding of how their signature providers are tracking their usage may find it valuable for the provider to directly link usage to identifiable agreements. The Send agreement information to the Cloud Signature Provider option provides three data elements to the signature provider when the signature application is attempted:

The AccountID - Your overall account identifier in the Acrobat System.
The GroupID - The specific group from which the agreement was sent. This is useful if different groups have different providers available or the accountID isn't configured to enable all groups with the same providers.
The TransactionID - The individual agreement-level identifier that gives the most granularity to understanding how signatures are consumed.

The Digital Signature configuration page with the "Send agreement information to the Clouod Signature Provider" option highlighted.

External signers are defined as any email address not within your Acrobat Sign account.

Internal signers being all of the users defined within your Acrobat Sign account

If you would like to create a different signature experience for external signers vs internal, you can enable a second set of the above options that apply only to external signers.

For example, you may want to be more permissive in the signature vendors for external signers, or provide different instructions for how to obtain a signature for internal signers.

The Digital Signature configuration page with the settings for external signers option highlighted.

Note:

Show Signing Reason

Some compliance requirements demand that a reason for an applied digital signature be noted by the signer. eg: Title 21 CFR Part 11 and SAFE-BioPharma compliance.

If digital signatures are being used to fulfill a compliance demand, consult with your legal team to determine if you should also require a signature reason within the signature process.

To access the controls, click the Bio-Pharma Settings link

If you need advanced signature controls, refer to the BioPharma page >

Things to know and frequently asked questions

RSA-PSS

RSA-PSS is a signature scheme that is based on the RSA cryptosystem and provides increased security assurance relative to the older RSA-PKCS#1 v.1.5 scheme.

The Acrobat Sign implementation of RSA-PSS does not require any configuration on the part of the Account Admin.

When “Cloud Signature” is chosen, and the signer’s Digital ID supports both RSA-PSS and RSA-PKCS#1, the RSA-PSS signature scheme is used by default.
When “Sign with Acrobat” is chosen, the use of RSS-PSS or RSA-PKCS#1 depends on the signer's settings in their Acrobat application
Acrobat Sign fully supports CRL and OCSP responses that are signed with the RSA-PSS scheme.
The use of the RSA-PSS scheme is required to comply with Germany-specific requirements for Qualified Electronic Signatures.

Digital Signature Format options

PKCS#7 is the default format governing the digital signature for most (non-EU) Acrobat Sign accounts.

Accounts on the European (EU1) shard use PAdES format (ETSI EN 319142) by default to meet eIDAS compliance.
Any account level admin can request to have this setting changed from one format to the other by sending a request to the Acrobat Sign Support team.
This feature can be enabled and configured at the group or account level.

The digital signature workflow forces the agreement into a unique process. Because of the special handling required to get the signature affixed, there are several limitations to be aware of.

Each signer can have only one digital signature field assigned to them when downloading the document and signing with Acrobat. Cloud-based signatures can support up to 10 digital signature fields per recipient. (Aadhaar and Singpass are not supported.)
Web forms don't support digital signatures.
Send in Bulk does not support Download and Sign With Acrobat signatures. Cloud-based digital signatures work as expected.
Digital signatures are not supported in Microsoft Office Desktop apps, as they're designed to work inside a browser environment. Alternatively, you can use the Office Web apps from your browser.
Digital Signatures disable Limited Document Visibility. All recipients will see all pages.
Signers on Mobile devices can only apply a cloud-based digital signature.
Cloud-based Digital ID using OAuth authorization mode are not supported in Fill & Sign feature.
Fill & Sign feature does not support signing with Aadhaar service provider.
Users sharing their content or accounts with advanced sharing enabled cannot use digital signatures.
eVaulting cannot be used in conjunction with digital signatures.
File attachments can only be applied by the first signer. Subsequent signers that attach new files invalidate all previous digital signatures.
If the Audit Report is attached to a digitally signed agreement, a PDF portfolio will be created using the two documents.
Transaction Number fields will convert a digital signature into an electronic signature.
If the option to attach the Audit Report is enabled, a PDF Portfolio will be created (containing the agreement and a separate PDF for the Audit report, both encapsulated within the PDF Portfolio, aka PDF Envelope) as once a Digital Signature is applied, no changes can be made to the agreement.

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Overview of Digital Signatures in Adobe Acrobat Sign