Here in Sunny Hollywood, entire industries have been created to prevent the reading of screenplays. Special software has been developed to format and outline screenplays. Massive fortifications are built around the screenplay readers. They are hidden inside glass towers with armed guards. A succession of receptionists, nested like Russian babushka dolls, exists to divert, befuddle, bamboozle, and otherwise detain and dissipatethe approaches of all screenplay deliverers. Special individuals, mostly rudderless alcoholic ivy-leaguers with liberal arts degrees, run what is called "Coverage." Coverage involves reading a screenplay and then filling out a form. The form can then be read in lieu of the screenplay! Man, we saved everyone a lot of time and kept an ivy-leaguer out of law school.
It's hard to blame them. A friend of mine once described to me a particular corridor over at Warner Brothers. It was a long hall, over 100m in length. It was lined on either side with giant blue plastic dumpsters - only slightly smaller than a full-sized building dumpster. These dumpsters were designed to be moved with a forklift. Each one was labeled. The labels corresponded with the first two letters of the screenwriter's last name. Every bin was full of screenplays. Untold hundreds of thousands of screenplays. My friend told me that these were the unsolicited screenplays that WB received EVERY YEAR. Look, if you don't have an invitation - don't come to the party. It isn't worth the wear and tear on your laser printer. People just won't read screenplays unless they absolutely have to.
So I can complain about it. I can be bitter. Many people more important and connected than me have complained and become bitter. It doesn't matter. It is only on the rarest of occasions that someone will read your screenplay first. What they will read, if you can penetrate the force field, if you can slip under the electrified wire and past the former Berlin Wall machinegunners, is your "treatment".
The full name is technically "Screenplay Treatment," but everyone just refers to them as "treatments". A treatment is a 5 to 20 page prose retelling of your screenplay. They used to drive me nuts. I mean, if I could have told the story in 20 pages, wouldn't I have stopped at 20 instead of going on for another 80 pages? I got over it. Writing treatments is an unavoidable reality, so make it work for you. It is a sales tool. It is a 5 minute window into your reader's mind. Trust me, they WANT it to be good. All day long, they want something GOOD to come across their desk, because every fucking thing they read is crap. Why? That is a discussion for another time.
So just write 15 pages of solid storytelling. You have to figure out how to get your much larger story into a smaller package. If you are a good enough writer to write a stellar screenplay, then you are a good enough writer to sell you story in 10 pages. You don't have to tell it, just sell it. Evoke the feeling of the story. Set the scene. Make them want to get more of what you're selling. It's like demo software - you only have to show them enough to make them upgrade to the whole enchilada.
Look on the bright side - it's prose! No hinky screenplay format! You can pretend you're Don Delillo. You can pretend you're James Ellroy. You are writing a text trailer for your movie, before the director and his nabobs get their mits on it and fuck it all up. Make it exciting. Grab your reader by the short and curlys. There are no real rules other than hit your plot points, go long on the sizzle, and don't get too far out stylistically.It has to be a fast, fun, easy read.
Even if they don't want your particular idea, if they like your treatment, producers will often ask to see other things you've done. So it's always good to write up as many ideas as you can. You need to have a squadron of these things. Fecundity is respected in Hollywood.
If you're lucky, you can sometimes sell just the treatment. You're basically selling the idea and basic trajectory of the story. Congratulations! You were just paid several thousand dollars to write a 5 page story idea.
Some folks worry about showing their hand with the treatment, and then getting their idea stolen. You should keep a log of who you talk to a when. Keep fax transmission reports and email. Honestly, you should be so lucky as to have them steal your idea, because the lawyers will be lining up to help you sue. So don't sweat it.
For an example, look here: Dreamland: a screenplay treatment