The biggest thing that costs us time is schema validation. We ended up building a tool that rejects uploads if the text fields don't match, or if you forget to include a radio option, etc. It also has "recommended" fields which issue warnings if they are not implemented.
Radio options, checkboxes, and images (for signatures) would be a welcome addition that I didn't see in the editor.
The documentation / online demo doesn't make it clear how I would go from fields -> API access (because how do I name the fields?).
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An API endpoint to get the unfilled PDF template would also be good, especially if bundled with a client library that handled the call to pdftk. Some of our documents are HIPAA and I don't want to deal with having the client data leave our machines.