Brazilian e-signature API with a free plan.
Assinafy API is a free Documents & Productivity API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from api.assinafy.com.br.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Online file converter for audio, video, document, ebook, archive, image, spreadsheet, presentation
The Assinafy API is provided by Assinafy API Reference (api.assinafy.com.br).
Yes. The Assinafy API is listed in the Documents & Productivity category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Assinafy API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Assinafy API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Assinafy API is served over HTTPS, so it's safe to use in production.