If someone sent you a file encrypted with this site's Encrypt File tool, Decrypt File restores it to its original form using the password you were given, entirely on your own device.
Either the password is wrong, or the encrypted file was altered or only partially downloaded. The two cases look identical by design, since telling them apart would leak information about the password itself. Double check the password and that the whole file transferred correctly.
Yes. The original filename and file type are stored (encrypted) alongside the file's contents, so decrypting restores both automatically.
No. Decryption happens entirely in your browser. The encrypted file, the password, and the decrypted result never leave your device.