How long a signature in a PDF stays verifiable depends on its profile. PAdES, the PDF Advanced Electronic Signature profiles, is the name that requirements for archives and electronic signatures refer to. A basic signature can be checked reliably while the signer's certificate is valid. A signature with a trusted timestamp can still be checked after the certificate has expired. TX Text Control creates both with the same DigitalSignature class; the difference is a time server URL.

Adding a timestamp is described in Add a Trusted Timestamp in Getting Started, and the time server itself in RFC 3161 Timestamps.

PAdES-B and PAdES-T

A common misconception is that all digitally signed PDF documents offer the same long-term trust. Two profiles show the difference:

	PAdES-B	PAdES-T
Contains	The digital signature, the signer's certificate and its certificate chain	Everything in PAdES-B, plus a trusted RFC 3161 timestamp
Verifiable right after signing	Authenticity and integrity	Authenticity and integrity
After the certificate expires or is revoked	A validator may be unable to determine whether the certificate was valid when the document was signed	The timestamp proves that the signature existed while the certificate was valid

Technically, the only difference is the timestamp token. For documents that must remain verifiable for years, such as contracts or archived records, it's the part that makes the signature last.

What TX Text Control Creates

TX Text Control signs a PDF or PDF/A document when it's saved with a DigitalSignature in SaveSettings.DigitalSignature or SaveSettings.SignatureFields. The time server URL of the DigitalSignature is the only choice that affects the profile:

Without a time server URL, the signature contains the signing time from the clock of the computer.
With the URL of an RFC 3161 time server, TX Text Control embeds a trusted timestamp in the signature. Text Control describes such a signature as conforming to the PAdES-T profile.

DigitalSignature has no members besides its constructors, so there is no setting for a profile, a hash algorithm or validation data such as revocation information. When a contract, a regulation or a recipient requires a particular PAdES level, check signed sample documents with the validator that the recipient uses before you rely on them.

Specify the Time Server shows the values of the time server URL, and Adobe Acrobat Reader states in its Signatures panel whether a signature includes an embedded timestamp, as How Readers Show the Timestamp shows.

PAdES and Electronic Signature Levels

In the European Union, the eIDAS regulation, Regulation (EU) No 910/2014, is the primary legal framework for electronic signatures and trust services. Legal requirements usually describe signatures by their level of assurance:

Level	Characteristics
Simple electronic signature (SES)	Typed names or check boxes, for example
Advanced electronic signature (AES)	Uniquely linked to the signer, able to identify the signer, created with data under the signer's sole control and linked to the signed data so that later changes can be detected
Qualified electronic signature (QES)	Based on a qualified certificate from a trusted provider and created with a qualifying signing device; under eIDAS, it has the same legal effect as a handwritten signature

Which level a document needs depends on the jurisdiction and the process. The level also depends on parts of the process outside the PDF: TX Text Control captures electronic signatures and applies digital signatures, while your application provides parts such as issuing certificates, identifying signers with a login and two-step verification and recording data such as IP addresses. The blog article The State of Electronic and Digital Signatures (E-Signatures) in Business Applications (2025) gives an overview of the frameworks in the European Union and the United States.

PAdES and PDF/A

PDF/A keeps a document readable for the long term, and a timestamped signature keeps its integrity verifiable. A document saved with StreamType.AdobePDFA and a DigitalSignature with a time server URL combines both, as PDF/A, PDF/UA and Digital Signatures describes.

Check a Signed Document

Adobe Acrobat Reader and the TXTextControl.PDF.Validation package check signed documents, as Signature Validation describes. The blog article Building Long-Term Trust with Digital Signatures and Timestamps in C# .NET explains the profiles and the role of timestamps in more detail.

Next Steps

RFC 3161 Timestamps: add trusted timestamps and handle unavailable time servers.
Certificate-Based Signatures: use certificates from a trusted certificate authority.
Signature Validation: check signed documents in code.
Compliance: the security and compliance topics of TX Text Control .NET Server.