Where does the hash come from?

[radix]

I have a notepad file with a single word in it that I encrypted using Blowfish encryption with the password 12345 and now I want to use Hashcat to decrypt it to see if I'm doing it right. Where do I get the hash from to obtain 12345 as the output crack?

You have

1) encryption<=>decryption
You can go backwards and forwards if you know the encryption key

2) One way message digest (hashing)
There is no key involved generally speaking, the same input will always result in the same output (aka the hash). To 'output the crack' you are actually running in different inputs and trying to obtain that same output, you are not decrypting but searching for hash collisions.

You are probably confused because some algorithms are used in both hashing and encryption/decryption, while the algorithm may be the same the process is altered making them different. You cannot decrypt hashes, otherwise that would defeat the whole purpose of them.

tl;dr You cannot find the hash for your encrypted notepad file since encryption/decryption is different to one-way hashing.

Are you saying that Hashcat cannot do anything, even brute force, to obtain the password to an encrypted file, even when the encryption algorithm is known?

no it cant.