PdfDigitalSignatureTrustedCaCertificates Property

Gets or sets an optional set of additional trusted certificate authority certificates, as DER encoded X.509 certificates. They complete the chain of a Certificate and, when producing PadesBaselineLT or PadesBaselineLTA signatures, the signer and timestamp certificate chains whose issuers cannot be located through the Authority Information Access extension of the certificates

public byte[][] TrustedCaCertificates { get; set; }