Hello. Signing PDF documents online without third-party software is not only possible but also quite convenient. Many operating systems, including Windows and Mac, have built-in tools allowing you to add your signature directly to a PDF. For a seamless experience, explore your system's native options. Additionally, when dealing with necessary documents, a handy tool is PDFLiner. It's a versatile PDF reader and editor, and it simplifies the process of sending a PDF for signatures(
https://pdfliner.com/send-a-pdf-for-signature). This way, you have control over your documents without relying on external applications.