Filing with the court means that the document (to be filed) has been properly filed with the court. Each such document must have been served onto the other party first. So we will discuss the service of the document first.
Certificate of service basically means that you certify that whatever you are filing with the court has also been delivered to the opposing party. It wouldn't be a fair process if one party files some request with the court, and the other party doesn't even know such request was filed, and then it is granted.
Certificate of services, and thus delivery of the pleading is governed by C.R.C.P. 5. Do not think you can just mail things, or hand it over and it's all good.
The reason we discuss certificate of service here, at the beginning, is because every single filing has to be delivered and certified, otherwise it will not be valid. And if it is not valid, it appears as it does not exist. And if you have 21 days to respond to something, and it is not valid, then it doesn't exist and you do not get a second chance.
Few rules:
Who to serve:
If the other party has an attorney, you must serve the attorney, not the person the attorney is representing.
If the other party does not have an attorney, you must serve that person. Having said that, we will call the other party "opposing party" regardless of the situation and it will refer to the person you must serve. Obviously, if you are initiating the case you must serve the person as that person does not have an attorney yet.
How to serve:
If the opposing party is subscribed to your case through Colorado court online portal, then the service is done automatically and you do not have to do anything. If they are not subscribed then you must serve them (most practically by USPS certified mail). In either case, your certification must state what you did.
Initial Delivery
If the case does not exist in the court system yet, meaning you are initiating it, then you must deliver the initial pleading (we'll address what exactly) by a third party (you cannot do it yourself - nor by mail). Honestly, just hire a commercial server like https://www.trailfinderinc.com/serve
These parties know how to do it, and nobody will question it. Once served, you can file the pleading (along with the certificate of service you will receive from the server) with the Court.
If you can't get it served (like you don't know where the other party resides), then that's a quagmire we don't know much about. Read CRCP 5 to see what to do in that case, or consult an attorney just for this specific step.
If you are on the receiving end of this delivery, then you "have been served". The other party must file those papers you received (along with a certificate of service) to the court which will then initiate the case - and case number will be issued. After you were served, you have certain number of days to respond. We will talk about how and where to respond. The certificate of service is required in your response as well, and in every single pleading you will ever make.
Subsequent Service (after the case was opened)
Once the case has been started, and filed with the court, case number issued, any pleading (including the response to the initial pleading) must be served as well. However, you no longer have to hire professional servers to do it.
As stated above, if the opposing party is subscribed to your case in the online portal, you do not have to do anything except stating so in the certificate of service (see below). If they are not subscribed to your case in online portal, then certify that you are serving by USPS certified mail (see below) and print the pleading, mail it to them, and then file with the court.
How do I know if the opposing party is subscribed to the Online portal?
If you have access to the online portal (if you do not, then get one) check who is subscribed to your case. If you see opposing party there (whether the attorney or the person itself), then you do not have to serve at all as it is done automatically. Alternatively, you can go to the court house clerk's office, give them your name (or case number) and they can tell you who is subscribed to your case.
What is a certificate of service? What does it look like?
All it is, is a statement how did you serve the pleading to the other party. So, at the end of your pleading (after your signature of the pleading), simple add the following verbiage:
CERTIFICATE OF SERVICE
I hereby certify that on the date of filing of this pleading with the Court, a true and correct copy of the above was served to the [Petitioner or Respondent]. as follows:
Served via ICCES:
[Name]
{Your Name}
By: /s/ Your Name
[Your Name]
[Petitioner or Respondent]
*Signature on file in accordance with C.R.C.P. 121 § 1-26.
That's it. The ICCES means the online portal. If you serve by mail, then simple state "Served by USPS Certified Mail:" and include the exact mailing address where you mailed it. It must match with what is on the record with the Court.
For signature itself, you can either print and sign (then scan back if you are filing online), or you can type /s/ and your name, like in "/s/ John Doe".
So yes, your pleading will have two signatures. One for the pleading itself (we'll talk about that later) and the certificate.
Filing with the Court
Once the pleading has the certificate of service, you can file it with the court.
If you have an online system, simple log in and file a document with the court. The system will guide you how to do that. You will need to give the document a proper type (although court clerks usually fix mistakes), like a motion, or response, or reply, or notice, or report, etc...
If you do not have an online system access, then get one. But in this case you can print your pleading (2 copies best, although 1 is enough) and bring it to the court house. Give it to the clerk, who stamps both copies and files one. The other one is for you to keep. It's as simple as that.
The online portal is way more convenient, although there is a fee involved with each pleading.