What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Am I right that you want to fill a value on some specific column of the matrix field that can' t be edited? Unfortunately, it's not possible with the matrix table in the form builder but you can take your form source code and apply a constant value. http://www.jotform.com/help/104-How-to-get-the-Full-Source-Code-of-your-Form
There is actually a workaround by prepopulating values on the matrix field but this is editable on the form. http://www.jotform.com/help/71-Prepopulating-the-fields-to-your-JotForm-via-URL-parameters
Let us know if you need further help. Thanks!