So many NetSuite added objects in the Advanced PDF templates aren't of type Extended Hash and so don't support listing their keys. However you can find the listing of the key values in these special objects here: https://netsuite.custhelp.com/app/answers/detail/a_id/73900. This information should be spread far and wide and to every Developer or Consultant who has to touch Advanced PDFs. There could be man-years of time saved!

I normally use the Records Browser (2021.1 version out now) Do you find this to be better? Also finding the Records Catalog great as it includes fields from enabled features

@David B No, not better when doing up Advanced PDFs but instead in addition because it's already essential when doing any work with record fields which is likely in the same space. The records browser is well known and required learning for novice developers in general to find supported fields inside of record objects however here my link was for special non-record objects specifically found in some templates that are native NetSuite. An example is 'statement' when generating a statement which uses an Advanced PDF. The list of their contents is found in my original link for this thread. Finding this list is a little more out of the way, it's buried with the history of being implemented through SuiteBuilder. You also can't dump it out programmatically like most would rely upon being able to do because the implementation with Freemarker was not doing a data structure that allowed that, which I would wager has caused a lot of frustration for developers who weren't involved with SuiteBuilder. Great job on the NetSuite Field Explorer @michoel! Been using that too for some years.

Thank you, happy you find it useful

statements! of course! I've seen so many questions around statement templates