HOW TO : Protect my file by password or encryption

The first protection level is you; then it is your computer user data which is supposed to be isolated from other users. That's the case under MS Windows and under GNU/Linux and most other systems (for MS windows, all users should not be Administrators, if it on your computer(s)... then it is the time to change this).
If you Google to find out how to protect you file on a family shared computer, you will find plenty of article on how to do this.

If you feel that your personal finance require additional level of security, there is plenty of solutions to encrypt data on a computer (TrueCrypt, PGP, native windows bitlocker) for that purpose.

A financial application should manage finance data, and a security program should deal with security. Any software must have some scope limits. I think it is better to use external proven and reliable solutions than implement a smokescreen, as the file format used for HomeBank to store data is a simple xml file (so text file), you can review with a txt editor.

Adding to this, I do think it make sense and it is more convenient to protect data globally on a computer, instead of being annoyed to fill in a password every time you open a file with an application, your session password and a truly global protection system on your computer should be sufficient.

At last, this enable users to choose the security solution that fit their security level needs and the way they protect their data's.