Both eSignatures and seals use electronic certificates to make the document verifiable and protect it against tampering. But the use case is quite different for each of those features.
Here are the main differences to help you decide whether to sign or seal your document.
A digital signature consists of 2 parts - an electronic certificate and a visual image. A certificate can be personal or issued per organization. The image (signature) is then usually personal, although can be representative of the whole organization as well (stamp).
The certificate component in a signature is mainly for protection, and the image component indicates an agreement (i.e the individual or company signed confirms their agreement with the content of the document).
On the other hand, a seal is invisible in a document, as it only consists of the electronic certificate and has no visual representation. The presence of a seal can only be detected through selected PDF readers such as Adobe Acrobat, or a specialized verification tool.
The main purpose of adding a seal to a document is twofold:
1) protect the document against unauthorized changes, make it verifiable online
2) confirm the origin of the document - it originated from the organization or individual who owns the electronic certificate
A seal does not indicate an individual's or organization's agreement with the content of a document.
Last but not least, sealed documents can be signed at a later date. Signed documents, however, are considered completed and cannot be further processed nor sealed.