The PDF/a Standard
For long-term PDF storage, the new PDF/A standards are used. PDF/A stands for PDF Achieve and is defined by the new ISO 19005-1 standard. The ISO 19005-1 standard is a standard for digital document applied to their long-term preservation. PDF/A format has been created keeping all things in mind so that it does not end up as an incompatible or legacy format as the PDF technology further evolves. By using the PDF/A format for archiving, it will become possible to retrieve, search, view, reproduce, and print archived documents in future with the full legal fidelity of the original. PDF/A is a subset of PDF that is created by removing those features from PDF that are not conducive to long-term archiving of documents. If your files for PDF storage are generated by using a product that is fully compliant with the new PDF/A standards, then the files will remain available for ever just like the original files.
How It Works
PDF/A is self-documenting, self-contained, and device-independent. It is transparent to direct analysis by using basic indexing tools etc. It enables us to conserve electronic documents with their visual appearance that can be recreated with no dependence on the systems, technology, and the tools that were used for their generation, storage or rendering. According to the PDF/A standards, the document cannot rely on information being called from external sources, whether they are indirect or direct sources. In effect, all ingredients needed to make sure that the document can be produced at any time in the exact same manner again and again have to be part of the document, they have to be embedded into the document.
Drawback of the PDF/a Standard
One drawback of PDF/A is its requirement of embedding all the required fonts and not calling any font form outside the document. This requirement increases the size of the document and if you are archiving a group of small files that use the same font, you will need to embed the font in each of the files. Another disadvantage is that that transparency is forbidden in PDF/A-1. Therefore, PDF generation tools that are also PDF/A document compliant will have to make all the transparent images in a document non-transparent.