You may have saved that file without noticing it if the desktop is your default download location.
You can check the download history in the Download Manager.

• https://support.mozilla.org/kb/Downloads+window

In that case you can remove the file.
You can inspect the file with a text editor to see if you can find out where it came from.

Thank you for your answer. As it turns out I did not have a printer available to me so in fact I did save something to my desktop and forgot it. I was afraid to open it not knowing what it was but when I opened it I realized I had saved it for proof of payment.

Thank you for the quick response

You're welcome