Each project has its own documents in SharePoint.
For creating the Project documents, first of all we have to create context by passing the projectSiteUrl.

1. Create context of projectSiteUrl

using Microsoft.SharePoint.Client;
context = new ClientContext(projectSiteUrl); //pass your project site url
context.Credentials = projectContext.Credentials;

2. Find list using list name

List spList = context.Web.Lists.GetByTitle("Documents"); 

3.Add documents to lists

if (spList != null)
	{
			try
			{
				byte[] content = System.Text.Encoding.UTF8.GetBytes("FileLeafData");
				Microsoft.SharePoint.Client.File f = spList.RootFolder.Files.Add(new FileCreationInformation() { Url = "Project.docx", Overwrite = true, Content = content, });
				ListItem newListItem = f.ListItemAllFields;
				newListItem["FileLeafRef"] = "Project.docx";
				newListItem["Title"] = "Test";
				newListItem["MetaInfo"] = "Your Meta Info";
				newListItem.Update();
				context.ExecuteQuery();
			}
			catch (Exception ex)
			{
				//log exception
			}
	}

Hope this code will help you.

Thanks