How can I see if the document is signed (validation)?
When you open the document with a PDF reader or browser you will see that the document has been given a front page that says that the document is signed. There you will find information about when the document is signed, by whom and what electronic ID that has been used. In addition there is a watermark on each page of the document. You will get an error if the signature is invalid.
If you are using Adobe Reader (PDF reader) you will get in addition to the signature on the front, and the watermark, get up a signature panel. There you can choose to view certificate information about the certificate used to sign PAdES document (the signed PDF document). If the PAdES signature is invalid, you will get an error message. By opening the integrated attachment in PAdES, you will see the personal signature in .xml format (XAdES). In XAdES you will find both the personal signature, the original document as the personal signature is applied and a ttp-log (defined under the terms and concepts). The XAdES can be opened either in your browser, or with notepad. If the PAdES-document has been altered after signing, the signature panel will not appear and the integrated XAdES attachment will be gone, so that the document validates as a regular PDF (and not as PAdES).
If the original document is in .txt, the signed document can only be viewed as XAdES.