One increasingly popular way to avoid the problem of obsolete file formats is to use XML as a source file format. XML is based on ASCII text or Unicode, which are readable by a large number of software applications, and will continue to be readable long after today's proprietary binary file formats have inevitably been replaced by newer proprietary file formats.

XML will likely be readable long into the future. However, the XML file format typically stores content, not formatting information. We may also want to ensure that a document can be read in its original format, long into the future.

To address the issue of preserving document content and format, the International Standards Organization (ISO) has published a standard for supporting the long-term archiving of digital documents. This standard, known as PDF/A (PDF/Archive), is based on Adobe's Portable Document Format. A PDF document that conforms to the PDF/A standard will be readable, with no change in format, by future software applications that support this standard.

The PDF/A standard specifies characteristics of the PDF file to ensure that it will be readable long into the future. Among other items, all fonts must be embedded. Embedded programs or scripts are forbidden. File attachments, even PDF job options, are not allowed in a PDF/A document.

Adobe Acrobat 8 Professional "Preflight" option (Advanced->Preflight) provides the capability to convert a PDF document to PDF/A. Acrobat 8 will inspect the document for conformance to the standard, and report any errors that you must fix.

PDF/A is certainly not appropriate for all PDF documents, nor is it necessary for documents that are likely to have a relatively short lifespan. However, if you are creating documents that should be available and readable for years or decades, you might consider using the PDF/A standard.