Is it possible to give legally acceptable digital signature with other programs?

Many programs (Microsoft Word, Open Office, Thunderbird, Adobe Reader) offer the possibility to give digital signature/signing the document. Unfortunately these signatures are not legally valid, as there is no validity confirmation. 

Digital Signature law on paragraph 2 page 3 point 2 says: “Digital signature along with the system used to give it, must allow to verify the time when digital signature was given”. Timestamps and validity confirmation service are effective ways to achieve that. Only adding the time when digital signature was given is not enough, as it is possible to forge that (for example by changing the computer’s date or time), that’s why it is needed to use the independent service provider (like Certification Centre). 

So we advise to use DigiDoc programs or to give digital signature in portal.