Is it possible for a user to sign his/her own signature even he/she doesn't have a DocuSign account? In the github code example (https://github.com/docusign/qs-csharp) I found that account id is passed in parameter. So please let me know how it is possible to sign without docusign account. If possible, please share any specific code example/ api link/demo that can be helpful.
Yes, it is possible. the account in this example (accountId parameter) is for the API call. Someone (the sender) has to have an account. But signers of your code do not need to. Again, you specify one accountId, for the overall account and then just have other users sign - they do not need an account. try this code example - https://github.com/docusign/code-examples-csharp but make sure you create your Integration Key and use OAuth correctly.