Can I trust PDF validation software?
If I use validation software from different manufacturers I sometimes get different results. Why can this happen? Does it mean that I can't trust the software? What can I do about it? I hear these and more questions very often and I can understand the user's concerns. In this article I try to shed some light on the mysteries of PDF validation.
What is a PDF Validator? That's a software which checks the conformance of a PDF document with a particular specification such as PDF-1.4 or ISO-32000 (PDF-1.7) or ISO-19001 (PDF/A) etc. There are a number of independent PDF Validator suppliers, including Adobe with its Preflight function as part of its Acrobat Professional Edition.
Which checks does a PDF Validator perform? A PDF Validation software usually offers a number of rule sets (sometimes called profiles). The user can select a rule set and check his document for conformance with the particular rule set. The number of rules and the nature of the checks depend on the software. If for example a rule set is named PDF/A-1b this does not mean that all validation products use the same set of rules. There are various reasons for this:
Some validators concentrate on the rules given by the ISO standard and neglect the rules of the related documentation (e.g. PDF-1.4 in case of PDF/A-1b) whereas others are going further.
The interpretation of an ISO standard is not as easy as it seems and experts may sometime have a different opinion.
Some rules are not part of a published ISO standard (e.g. the format of an embedded TrueType font).
Some rules might have been forgotten or misinterpreted.
How can I check the quality of a PDF Validator? There are a number of test suites on the market to test the validation software. As an example, the PDF Association released the Isartor Test Suite which is intended to test a PDF/A-1 validation software. The PDF Association is currently developing a test suite to cover PDF/A-2 und PDF/A-3 as well.
If I still have different results even if both validators pass the corresponding test suite, what does this mean? As with validation software a test suite cannot cover all real world cases and is undergoing continuous maintenance to improve it.
What can I do if I experience different results? In this case please send a support request to the involved manufacturers and mention which products you used. This enables the manufacturers to solve the issue in a bilateral way. If the case is more complex and if the manufacturers are members of the PDF Association then the case will most likely be submitted to a technical working group to be solved.
And, to let this article not grow too long, here's my conclusion:
PDF validation software which conforms to the test suites of the PDF Association have good quality and are continuously improving.
It is in the interest of all serious manufacturers, especially those that are PDF Association members, to harmonize the validation results.
There are still differences in the validation results but these differences are often related to a harmless cause.
A user can help to improve the situation by following the process described in this article.
