string siteUrl = "http://servername:12345/";
SP.ClientContext ctx = new SP.ClientContext(siteUrl);
ctx.Credentials = new SharePointOnlineCredentials(userName, passWord);
this.ctx.Load(this.ctx.Web);
SP.Web web = this.ctx.Web;
SP.File file = web.getFileByServerRelativeUrl("serverrelativeUrlOfTheFile");

//CheckIn the file
file.CheckIn(String.Concat("File CheckingIn at ", DateTime.Now.ToLongDateString()), SP.CheckinType.MajorCheckIn);

//CheckOut the File
file.CheckOut();

//Publish the file
file.Publish(String.Concat("File Publishing at ", DateTime.Now.ToLongDateString()));

//UnPublish the file
file.UnPublish(String.Concat("File UnPublishing at ", DateTime.Now.ToLongDateString()));

Remember, before making any changes to the state of the file it is always advisable to first check its current state/level. You can check the current state of the file i.e., if the file is currently CheckedOut, Drafted (CheckedIn), OR, Published. You can easily do that by checking the FileLevel value of the file you’re querying. FileLevel is an enum which specifies the publishing level for a file. MoreInfo

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