Sign and fill
The documents that should least like being uploaded.
About these tools
The documents people sign are the most sensitive things they will ever put through a web tool. Leases, offer letters, medical forms, tax paperwork, contracts carrying a counterparty's terms. The ordinary way to sign one online is to upload it to a stranger's server and trust a retention policy written by their lawyers.
There is no retention policy here, because the file is never received. The document is opened by the page, changed in memory, and written back out as a download. You can verify that in a few seconds with your browser's developer tools open.
What these tools produce is an image of a signature composited onto the page. That is legally the same instrument as signing a printout and scanning it, and it is treated as a valid electronic signature for ordinary agreements under the US ESIGN Act and eIDAS in the EU. It is not a certificate-based digital signature, and there is no cryptographic proof of who signed. If a counterparty specifically requires that, you need a qualified provider instead. Saying so plainly is more useful than letting you find out at the wrong moment.