Zyox,
Welcome to Bladeforums. I changed your title to make the thread more on topic of what you want to know.
What you want to do will leave the blade soft and useless as a knife. It will remove all of the hardness. Just getting it orange and sticking it in a bucket of oil would probably not be good to try and harden it again. Water would break the blade in tow or tree pieces. The stickys has lots of heat treatment info which should explain some of what you need to know.
BTW, orange is a color of hot steel far above what you harden at. The colors are sort of arbitrary, and everyone sees them different, but there are charts of "steel colors" that tell approximately how hot it is, These are OK for forging, but bad for doing HT.
The stickys has a section on Making a knife from a file, which has most all the info you need for your project. It also has a section called "How to Instructions for Making a Knife". That will likely help you a lot. Read all the stickys to get a basic idea of what is involved in making knives. The ones on metallurgy and HT are really important to know.
The basics answers to your question are:
To make grinding and shaping the file easier, you need to make it less hard. There are two ways to do that.
One is to work the file in the hardened state,.... but slightly less hard than it is now, because a file is too brittle to make a good knife blade. You temper the file to remove the excess brittleness. (see below on tempering).
The second, and best method is to anneal the file. This is done by heating the file up to a dull red color and allowing it to cool slowly several times. This changes the file to a softer structure. You can now file, grind, sand, and drill holes easily in the softened file. Once the shaping is done, you re-harden the file ( see below on hardening).
Steel changes its atomic arrangement ( called its "structure") around 1420F. At the same point it stops becoming magnetic. Using a magnet will tell you when your hot steel is around 1420F. Get a welding magnet or some other strong magnet and place it next to where you are heating the blade. Touching the blade to the magnet will tell you if it is below 1420F. When it crosses that point it will suddenly stop sticking to the magnet. You heat it just a shade of red brighter to 1475-1500F and then quench it in warm oil. Canola oil is the preferred simple oil. There are special commercial oils that bladesmiths use, but a gallon of Canola oil from the grocery store works quite well. Don't used old motor oil, it is a poor quenchant and has bad fumes. When you quench the knife, plunge it straight in the tank of oil ( use a steel pail or tank...not plastic!) and keep completely under the surface for 30-60 seconds. If you pull it out too soon, it may ignite the oil as well as affect the HT.
Once the blade is hardened, the structure is still not right. It will be very brittle, and can snap in two easily. It needs to be tempered. Your kitchen oven works fine for tempering. Pre-heat the oven to 400F and wash the blade off well to remove all the oil from the quench. Set on the shelf/rack in the middle of the oven. Tempering converts the structure to a much tougher state. You temper most all knife blades around 400F. Do it for one hour, cool off in water ( stick it under the running tap), and return to the oven to temper again for a second hour. After this, it will be ready to finish the sanding and make the knife.
This is the Bladeforums custom search engine. It will help you hind all kinds of information. A search for "making a knife from a file", "how to harden a blade" or for "HT on 1095" will give you lots of things to read.
https://cse.google.com/cse/publicurl?cx=012217165931761871935:iqyc7cbzhci
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