Adding a certified signature field to a PDF on iOS
To add a certification signature field to a PDF document and sign it:
PTPDFDoc* doc = [[PTPDFDoc alloc] initWithFilepath: docpath];
PTPage* page1 = [doc GetPage: 1];
// Create a text field that we can lock using the field permissions feature.
PTTextWidget* annot1 = [PTTextWidget Create: doc pos: [[PTPDFRect alloc] initWithX1: 50 y1: 550 x2: 350 y2: 600] field_name: @"asdf_test_field"];
[page1 AnnotPushBack: annot1];
/* Create a new signature form field in the PDFDoc. The name argument is optional;
leaving it empty causes it to be auto-generated. However, you may need the name for later.
Acrobat doesn't show digsigfield in side panel if it's without a widget. Using a
Rect with 0 width and 0 height, or setting the NoPrint/Invisible flags makes it invisible. */
PTDigitalSignatureField* certification_sig_field = [doc CreateDigitalSignatureField: cert_field_name];
PTSignatureWidget* widgetAnnot = [PTSignatureWidget CreateWithDigitalSignatureField: doc pos: [[PTPDFRect alloc] initWithX1: 0 y1: 100 x2: 200 y2: 150] field: certification_sig_field];
[page1 AnnotPushBack: widgetAnnot];
// (OPTIONAL) Add an appearance to the signature field.
PTImage* img = [PTImage CreateWithFile: [doc GetSDFDoc] filename: appearance_image_path encoder_hints: [[PTObj alloc]init]];
[widgetAnnot CreateSignatureAppearance: img];
// Prepare the document locking permission level to be applied upon document certification.
[certification_sig_field SetDocumentPermissions: e_ptannotating_formfilling_signing_allowed];
// Prepare to lock the text field that we created earlier.
NSMutableArray<NSString *> * fields_to_lock = [[NSMutableArray<NSString *> alloc] init];
[fields_to_lock addObject:@"asdf_test_field"];
[certification_sig_field SetFieldPermissions: e_ptdigsig_permission_include in_field_names: [fields_to_lock copy]];
[certification_sig_field CertifyOnNextSave: private_key_file_path in_password: keyfile_password];
// (OPTIONAL) Add more information to the signature dictionary.
[certification_sig_field SetLocation: @"Vancouver, BC"];
[certification_sig_field SetReason: @"Document certification."];
[certification_sig_field SetContactInfo: @"www.apryse.com"];
// Save the PDFDoc. Once the method below is called, PDFNet will also sign the document using the information provided.
[doc SaveToFile: outpath flags: 0];Digitally sign PDF files Full code sample which demonstrates using the digital signature API to digitally sign and/or certify PDF documents.
About certifying a PDF document
Unlike, approval signatures, there can be only one certification per PDF document. Only the first signature in the PDF document can be used as the certification signature. Certifying a document is like notarizing a document. The process of certifying a document is almost exactly the same as adding approval signatures with the exception of certification signatures requires an entry in the "Perms" dictionary.
About certifying a PDF/A document
If you want to certify a PDF/A document, it is best to convert to PDF/A first, then certify. This is because PDF/A changes the contents of the document, while digital signatures, including certifications, rely on the document's bytes remaining the same so that they can be digested and compared with the embedded cryptographic digital signature.
A DigitalSignatureField can be added before or after PDF/A conversion, since there aren't any requirements in PDF/A upon it.
The PDF/A-2 specification allows adbe.pkcs7.detached and adbe.pkcs7.sha1 certification-type or UR3-type cryptographic digital signatures, with or without secure timestamps, with or without embedded revocation information, which must be signed if present. A single SignerInfo must be present. Attribute certificates must not be used. The PDFNet SDK's signing support is sufficient to meet the requirements of PDF/A-2 compliance if used properly.
There shouldn't be any problem with retaining PDF/A compliance after digitally signing a document, so long as there is no annotation appearance for the digital signature field, or there is an appearance and that appearance conforms to PDF/A, i.e. e.g. sections 6.3.2 and 6.3.3 of the PDF/A-2 specification (ISO-19005-2).
An additional limitation of PDF/A for digital signing is the implementation limit that says that a conforming file shall not contain any string longer than 32767 bytes. Sometimes, signatures with a large amount of data will cause the Contents byte string in the digital signature dictionary to exceed this limit.
The PDF/A-2 specification also mentions the following:
Here is what 6.3.2 and 6.3.3 say about the annotation:
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