PdfSignature Class

Namespace:
GemBox.Pdf.Forms
Assembly:
GemBox.Pdf.dll

A digital signature (PDF 1.3) may be used to authenticate the identity of a user and the document's contents. It stores information about the signer and the state of the document when it was signed.

public sealed class PdfSignature : PdfObject
Public NotInheritable Class PdfSignature
    Inherits PdfObject
Inheritance:
System.Object
PdfSignature

Properties

ContactInfo

(Optional) Information provided by the signer to enable a recipient to contact the signer to verify the signature.

Example: A phone number.

public string ContactInfo { get; set; }
Public Property ContactInfo As String
Property Value
System.String

Information provided by the signer to enable a recipient to contact the signer to verify the signature.

See Also

Content

Gets the content of the PdfSignature.

For public-key signatures, Content should be either a DER-encoded PKCS#1 binary data object (octet string) or a DER-encoded CMS binary data object.

For document timestamp signatures, Content shall be the TimeStampToken as specified in RFC 3161 as updated by RFC 5816. The value of the messageImprint field within the TimeStampToken shall be a hash of the bytes of the document indicated by the ByteRange and the ByteRange shall specify the complete PDF file contents (excepting the Content value).

public PdfSignatureContent Content { get; }
Public ReadOnly Property Content As PdfSignatureContent
Property Value
PdfSignatureContent

The content of the PdfSignature.

See Also

ContentsLength

Gets or sets the length of the Content (in bytes).

public int ContentsLength { get; set; }
Public Property ContentsLength As Integer
Property Value
System.Int32

The length of the Content (in bytes).

Date

(Optional) The time of signing. Depending on the signature handler, this may be a normal unverified computer time or a time generated in a verifiable way from a secure time server.

This value should be used only when the time of signing is not available in the signature.

Example: A time stamp can be embedded in a PKCS#7 binary data object (see 12.8.3.3, "PKCS#7 Signatures as used in ISO 32000").

public DateTimeOffset? Date { get; set; }
Public Property Date As DateTimeOffset?
Property Value
System.Nullable<System.DateTimeOffset>

The time of signing.

See Also

FileSectionDepth

Gets the depth of the PDF file section that contains the PdfSignature or -1 if the PdfSignature is not contained in any PDF file section.

public int FileSectionDepth { get; }
Public ReadOnly Property FileSectionDepth As Integer
Property Value
System.Int32

The depth of the PDF file section that contains the PdfSignature or -1 if the PdfSignature is not contained in any PDF file section.

Remarks

The depth of the last PDF file section is 0 because a PDF file should be read from its end. The depth of all previous PDF file sections is greater than 0. Previous PDF file sections exist if the PDF file was incrementally updated.

If the PDF file contains multiple PdfSignatures, the PdfSignature that is last applied should have FileSectionDepth equal to 0 and FileSectionDepth of all previously applied PdfSignatures should increase incrementally by 1. Otherwise, there might be one or more PDF file sections containing modifications that invalidate last applied and/or previously applied PdfSignatures.

In PDF viewer/editor applications, a PDF file section that contains a PdfSignature is usually called a Signed Version or Revision of a PDF file and the last PDF file section is usually called the Current Version of a PDF file. For more information, see View previous versions of a digitally signed document and Compare versions of a signed document.

note

A PDF file section that contains a PdfSignature could also contain other modifications that might invalidate previously applied PdfSignatures (for example, changing the content of a page) and a PDF file section that doesn't contain a PdfSignature could have modifications that do not invalidate previously applied PdfSignatures (see Digital Signature Workflows examples). This depends on the transform methods applied to the PdfSignature (exposed via the Locks property) that guide the modification detection analysis that takes place when the signature is validated. The modification detection analysis is a complex process (for more information, see StackOverflow answers How to Validate Changes and Allowed actions for certified documents and for signed but uncertified documents and Adobe technical white paper Adobe Acrobat 9 Digital Signatures, Changes and Improvements, especially its section "Allowed and disallowed changes") and is currently not supported by GemBox.Pdf when validating the signature via Validate() method.

Format

(Optional) A name that describes the encoding of the signature value and key information in the signature dictionary. A PDF processor may use any handler that supports this format to validate the signature.

public PdfSignatureFormat Format { get; }
Public ReadOnly Property Format As PdfSignatureFormat
Property Value
PdfSignatureFormat

A name that describes the encoding of the signature value and key information in the signature dictionary.

See Also

Location

(Optional) The CPU host name or physical location of the signing.

public string Location { get; set; }
Public Property Location As String
Property Value
System.String

The CPU host name or physical location of the signing.

See Also

Locks

Gets the set of PdfSignatureLocks that specify what changes, made to the document after the signature was applied, invalidate the signature.

If the value is null, then the signature does not specify a Reference entry.

To set the Locks, sign the PdfSignatureField with a PdfSigner whose AuthorPermission is not null or use any SetLockedFields() method before signing on a PdfSignatureField that holds the signature.

public IList<PdfSignatureLock> Locks { get; }
Public ReadOnly Property Locks As IList(Of PdfSignatureLock)
Property Value
System.Collections.Generic.IList<PdfSignatureLock>

The set of PdfSignatureLocks that specify what changes, made to the document after the signature was applied, invalidate the signature.

See Also

Name

(Optional) The name of the person or authority signing the document.

This value should be used only when it is not possible to extract the name from the signature.

Example: From the certificate of the signer.

public string Name { get; set; }
Public Property Name As String
Property Value
System.String

The name of the person or authority signing the document.

See Also

Reason

(Optional) The reason for the signing, such as ( I agree … ).

public string Reason { get; set; }
Public Property Reason As String
Property Value
System.String

The reason for the signing, such as ( I agree … ).

See Also

Methods

ComputeHash(PdfHashAlgorithm)

Computes the hash of the bytes of the document indicated by the ByteRange (the ByteRange should specify the complete PDF file contents, except the Content value) with the specified algorithm.

public byte[] ComputeHash(PdfHashAlgorithm hashAlgorithm)
Public Function ComputeHash(hashAlgorithm As PdfHashAlgorithm) As Byte()
Parameters
hashAlgorithm
PdfHashAlgorithm

The algorithm with which to compute the hash.

Returns
System.Byte[]

The computed hash of the bytes of the document indicated by the ByteRange.

Validate()

Validates the PdfSignature.

caution

This method validates only that the document has not been modified since the PdfSignature was applied. The signer's identity (its certificate validity and revocation status) is currently not validated.

public PdfSignatureValidationResult Validate()
Public Function Validate As PdfSignatureValidationResult
Returns
PdfSignatureValidationResult

An instance of a PdfSignatureValidationResult that contains a detailed error information for the status of the signature validation.

Inherited Properties

Metadata

(Optional; PDF 1.4) A metadata stream containing metadata for the component.

(Inherited from PdfObject)

Extension Methods

Examples

See Also