Yes, toggle "apply to all pages" before downloading and the stamp will be placed at the same position on every page. You can also leave it off to stamp only the page you're currently viewing.
自分のスキャンした署名や会社の印鑑をスタンプとして使用できますか?
Yes, switch to image mode and upload a PNG or JPEG of your scanned seal, signature, or logo. Transparent PNG backgrounds work best so the stamp blends naturally into the document.