/MaxLen for text fields does nothing?

The /MaxLen parameter is an entry in the COS field dictionary for a text field. It is the same as the "Fields.charLimit" property in JavaScript and the "Limit of" option on the Text Field Properties Dialog. In fact the Field Properties dialog is a good place to learn about how this parameter is used.

I take it you are write an application to generate a PDF, and that you have a PDF library of some kind? If you are not using a PDF Library you will need to become an expert on the internal PDF format.

Thanks for your response, Thom.

Yes, I am troubleshooting / maintaining an application that generates pdf 1.4 output.

And I'm stumped on this one.
From everything I've read (e.g. the PDF Reference Manual), adding the /Maxlen entry for an AcroForm text field should limit how many characters the user can enter in the form field.

Here is more detail on my pdf code for the text field:

11 0 obj
<<
/Type /Annot
/Subtype /Widget
/Rect [ 40 726 179 739 ]
/T (FillText1)
/FT /Tx
/DA (/TiRo 10 Tf 0 g)
/Maxlen 5
/F 4
/StructParent 1
>>
endobj

Very simple.
However, running this form in Acrobat Reader 9 allows me to type more than 5 characters, in fact the length seems unlimited and scrolls horizontally, ignoring /Maxlen.
(Other than that, the form works fine.)

Note that for this field, there are no field flags (/Ff), but it is a plain text entry field and doesn't need any flags. Do I need to add /Ff 0 anyway perhaps? Do I have to supply the NoScroll flag to enable /Maxlen to work?

I suppose I could write some javascript to capture keystrokes and do the counting myself, but it doesn't seem like that should be necessary.

Thanks for any advice - at this point I'd almost think it is a bug in Acrobat Reader 9, but I can't imagine that - this would be a pretty major bug!

Your example shows Maxlen, not MaxLen.

Thanks, George
That was it!
(I knew it had to be something SiMPle...)

Details, details!! Good catch George!