What do we call it when a document is to be written according to no particular predefined template?

A sentence I've translated from Russian:

The Applicant must also fill out a Technical Appendix (in free form) providing, as far as this is possible, the most detailed description of the consulting activity and the expected results (technical documents, study protocols, final reports etc.).

Here "in free form" means that the Appendix has no predefined template and no strict rules - it is up to the Applicant and his common sense to decide how to arrange the words on paper.

Is in free form the most common phrase for this?

The Miltitran dictionary lists a number of options for the original Russian phrase в свободной форме.

From the list provided by the Miltitran dictionary, i feel like:

"in any format"

Would the most appropriate here, and most likely to be universally understood.

In free form is a bit more loose and more usually used in an artistic context like @BoldBen mentions.

Maybe something like "no specific format required" could also work.