When a document has a digital seal, the size increases, since we add a chain of digital certificates.
This is done mostly because when you open a PDF with Adobe Reader, the entire certificate is validated through the Internet. But in case you don't have a connection, the validation is done using a chain of digital certificates that are added to the PDF (and makes the document increase in size).
In sum:
If the document contains a chain of certificates:
- You can validate the certificate even when there is no internet connection.
- The document will increase in size.
If the document does not have a chain:
- You can only validate the certificate when you are connected to the internet.
- The document will increase only a little in size.