With the HelloSign PHP SDK by HelloSign, developers can interact with the e-signature features of the API. Resources on GitHub include installation and configuration. To install, this project requires PHP 5.3+ and PHP cURL extensions. To configure, this work needs an Api Key, basic auth, or OAuth. By Chris Paul.
So, you're trying to share some files with someone who only has access to an old version of Word. Or maybe that Microsoft-hating friend of yours who only uses WordPerfect. Perhaps you want that old-school ebook to be an epub, rather than .lit. For any of these problems, there are desktop apps that work, of course. However, sometimes you want to be able to do that within a program. If so, Doxument and the beautiful Doxument API are what you need.