This document describes the LetterSigner software for digitally signing PDF documents. It allows signing documents by hand using a stylus or digitally using a smart card. Key features include signing and editing PDFs directly in the application, batch signing multiple documents, and integration with Microsoft Office. Supported signing methods include handwritten signatures, digital signatures using smart cards, and adding other data fields.

1. LetterSigner

2. Table of content
Table of content ........................................................................................................................................................i
1. Why use LetterSigner ................................................................................................................................. 1
1.1. Interoperability ...................................................................................................................................... 1
1.2. Main advantages of the LetterSigner .................................................................................................... 1
2. LetterSigner functionalities ........................................................................................................................ 2
2.1. Signing by hand with an electronic pen................................................................................................. 2
2.2. Signing digitally by means of a smart card ........................................................................................... 2
2.3. Integration with Microsoft Office .......................................................................................................... 4
2.4. Batch Signing ......................................................................................................................................... 5
2.4.1. PDF documents without PDF signature fields ................................................................................... 5
2.4.2. PDF documents with a PDF signature field ....................................................................................... 5
2.4.3. Signing process .................................................................................................................................. 6
3. Sample workflow of LetterSigner............................................................................................................... 7
3.1. Supported PKI hardware & suppliers .................................................................................................... 7
3.2. Signature capturing devices .................................................................................................................. 7
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3. 1. Why use LetterSigner
The LetterSigner application offers all the necessary features to sign your documents. To serve the broadest
possible market, the Portable Document Format (PDF) was chosen as the LetterSigner document format. Both
the “classical” handwritten signature as the digital signature may be used to sign documents. It is also possible
to add other data fields in a document to enter a date, or free text, like “read and approved”.
The LetterSigner software enables you to open, view, navigate and sign PDF documents directly within one and
the same application.
1.1. Interoperability
Signatures produced with the LetterSigner application can be verified using the standard Adobe Reader® and
Acrobat Reader®.
1.2. Main advantages of the LetterSigner
Green IT as there is no more need for paper
Fast time-to-signature
Both classic & digital signature are possible
Multiple manual and digital signatures can be saved by the system
The signature is visible on the displayed or printed document
Revision lock by the signature, so others will not be able to change your documents
Digital timestamp needed for electronic archiving following European regulations
rd
No other 3 party PDF reader is required
A broad range of Smart Cards or tokens are supported natively (PKCS11 interface), for these devices no
CSP (Cryptographic Service Provider) is required
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4. 2. LetterSigner functionalities
2.1. Signing by hand with an electronic pen
When using the LetterSigner software on a Tablet PC or a specific signing device connected to the PC,
documents can be signed by hand using the stylus. The look and feel of this manual signing process equals the
ceremonial aspect of signing a paper version. Drawing one’s signature is only allowed on predefined fields, the
rest of the document remains locked and unchanged. These fields are indicated by standard PDF form fields,
which can be added by LetterGen during the creation of the document. When saving the document, the
handwritten fields (signatures and text) are embedded into the PDF document. The electronic signature is
represented as a stamp and secures the document.
2.2. Signing digitally by means of a smart card
An electronic signature is a legally recognized electronic tool, which indicates that a person accepts the content
of an electronic message or a document.
Signing documents digitally is based on a Public Key Infrastructure. By means of PKI based smart cards, such as
the Belgian eID, a DIGIPASS CertiID from VASCO, a Keynectis token, a Certipost token, a Diginotar Certificate
etc.
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5. Along with this signature a certificate is added to the document to provide the identity of the signer. The
combination of the signature and the certificate delivers non-repudiative proof of the identity of the signer, as
well as a warranty for the authenticity of the signed document. Since the signed document is fully PDF
compliant both the document and the signatures can be displayed and validated by a viewer using Acrobat
Reader.
Any user that modifies and saves the document, after it has been electronically signed, will invalidate the
electronic signature(s).
On the LetterSigner the signed field will be shown as hereunder.
Once the signature is saved, it will display in a viewer (like Acrobat Reader) as follows. Also, if a document is
printed, the signature will be shown inside the document, proving the signatory's identity and document
integrity.
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6. 2.3. Integration with Microsoft Office
The LetterSigner Microsoft Word add-in can be easily installed using the Windows installer.
The LetterSigner add-in allows you to sign and certify PDF documents without any need to purchase additional,
expensive 3th party products. This dramatically reduces the Total Cost of Ownership (TCO) .
The LetterSigner add-in automatically converts any Microsoft Word document into a PDF document and places
the correct signing fields on the PDF document depending on the way you chose to sign (signing manually,
digitally or a combination of both). The LetterSigner application is then launched automatically, allowing you to
easily create a signed and secured PDF document.
The signing procedure can be carried out in one or multiple sessions (multiple signers), This allows you to
create a document in Microsoft Word, sign it yourself and send the document in PDF format to your
customer(s) for countersigning.
The LetterSigner software supports most Software Certificates and Smart Cards. Such as the Belgian eID, a
DIGIPASS CertiID from VASCO, a Keynectis K.Sign® token, a Certipost token, a Diginotar Certificate etc.
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7. 2.4. Batch Signing
The LetterSigner Batch Signer application allows autonomous digital signing of documents. The application runs
as a Windows service.
2.4.1. PDF documents without PDF signature fields
When a PDF document without a PDF signature field is supplied, a digital signature will be added to the
document without a visual appearance on the document. The validity of the signature will be indicated by
Acrobat Reader®.
2.4.2. PDF documents with a PDF signature field
When a PDF document with a PDF signature field, with predefined and configurable name, is supplied, a digital
signature will be added to the document as well as a predefined and configurable logo/stamp as a visual
representation of the signature.
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8. 2.4.3. Signing process
When the document to be signed is dropped in an input folder, the batch signer automatically starts signing the
document using the configured token. If signing succeeds, the signed file will be dropped in an output folder.
Should an error occur, the unsigned (original) file shall be moved to an error folder and an event describing the
error shall be written to the windows event log.
This process can be duplicated several times as shown in the picture below using different input, output and
error folders. However, only one document will be signed at a time.
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9. 3. Sample workflow of LetterSigner
(1) Create a PDF document with handwritten fields and digital signature fields.
(2) Visualization of the document in LetterSigner. Digital signature fields and handwritten fields are
highlighted.
(3) Either free text or a signature can be drawn in the handwritten fields. It is impossible to draw outside the
predefined region.
(4) When clicking on a digital signature field, a PKI based signature is added to the document using one of the
supported security tokens.
(5) Multiple digital signatures can be added to the document.
(6) The final document, with all handwritten and digital signature fields embedded in the document.
3.1. Supported PKI hardware & suppliers
Belgian eID
VASCO Digipass PKI keys
Keynectis K-Sign
Certipost
K.Websign®
3.2. Signature capturing devices
Topaz signature pad
Stepover signature pad
Wacom Bamboo pad
Tablet PC with Stylus
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