The print, sign, scan, email routine wastes twenty minutes and produces a crooked grey scan. You can sign the PDF directly, and the document never leaves your machine.
In most countries an electronic signature is valid for ordinary commercial agreements, and a signature drawn or placed on a PDF is a common form of one. Some documents are excluded almost everywhere, typically wills, property transfers and certain court filings, and some organisations insist on a specific signing platform for their own audit reasons.
This is general information rather than legal advice, and the rules vary by country and by document. If the agreement matters, check what the other side requires before you sign.
What this tool does is place your signature onto the page as part of the document. It is the on-screen equivalent of signing the printed page, and it is the right fit for the everyday agreements that make up most signing.
No, which is the main reason to sign this way. The document stays on your device from start to finish.
Sign one page, save, then run the result through again for the next page.
Upload it. A PNG with a transparent background sits on the page best.