When you first decide to add signed electronic documents to your workflow the tendency is to want to sign the document in the native format of the creating application. So people often think that they want to sign Microsoft Office files, emails and CAD files. However there are several considerations when it comes to actually deploying the system.
What are retention requirements? If these signed documents need to be accessible in 10 years is the Word document format an appropriate format for archive?
Who will be signing the documents, and where? The availability of viewing tools is critical, as the document will need to be viewed electronically.
These considerations often cause the direction to turn to standard formats for archive. One format that has become very popular in electronic document archiving is the TIFF standard, largely due to its origins in the scanning and archiving of paper documents. TIFF is readily viewable using many applications and has proven to be a durable specification, as has its cousin in the imaging world, JPEG. These documents are easily signed and displayed. Indexing and storing requires using metadata tags as these documents are not inherently searchable.
Text documents have significant advantages for indexing and searching, but raw text lacks the formatting and images that are critical parts of most modern documents.
HTML and XHTML are gaining in popularity. The problem to date has been using restrictions to insure that the document is consistently rendered by the multitude of applications that display HTML.
The newest standard to gain favor is the Portable Document Format (PDF). This specification, developed and popularized by Adobe through its Acrobat family of products, is based on widely adopted Postscript page description language with extensions to support embedding fonts and other information useful to make a truly portable, device independent document format. Adobe released the PDF specifications and the rights to use them royalty free, although Adobe still owns copyrights. They also worked together with the ISO, AIIM and NPES to create the PDF/A format for long term document retention. The PDF references are available from Adobe here, and the PDF/A specification is available from the ISO. More information on PDF/A can be found at the PDF/A Competence Center.
In practice we have found that many organizations are migrating to the PDF standard, for multiple reasons. Native PDF has several advantages over image formats, in that PDFs are readily indexed and searched. However the biggest advantage is the ubiquitous and free Acrobat Reader. The prevalence of this application insures that nearly everyone that looks at a PDF document will see the exact same document. Other important features are the strong document-centric format and integrated support for digital signatures and X.509 digital certificates.
In the future we will have a section on methods for developing esignatures for PDF documents.
Posted by Mike Ambrose 
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