Today I was trying to fix a problem in a section of a website that hadn’t been changed in roughly 5 years. The page in question retrieved data from a database and filled out an Acrobat form using FDF. Under some circumstances, Adobe Reader would generate an error message, “Expected a dict object.” Then it would freeze, and crash the web browser for good measure.
This site was built with ColdFusion, and used a then-freely-available library called PDFFormFiller.cfm (I can’t find any sign of it now) to generate the FDF code. After saving the offending FDF to a file (eliminating the browser as a factor), I started manually editing the code to see what happened.
The problem turned out to be parentheses appearing in the form data. FDF uses parentheses-delimited strings, and it was finding
) in the code and trying to parse what was left as FDF tokens. The solution was simple: just escape the parentheses as
In this case, I changed this expression:
I don’t know whether older versions of Acrobat Reader were more lenient about this or whether this site just never ran into anyone using parentheses before. Either way, there’s precious little useful information about this problem online. In case anyone else runs into it, this entry should help.