How can I embed a SQLite Database in a .NET DLL and then use it from C#?

This is not possible as such. What you could do is embed the db in your dll project and dump it to certain location on the file system (may be AppData?) and read and write from there. Having db sit directly inside the executable (or dlls) may not be a good idea in the sense it bloats the size of the application besides being technically infeasible.

Having a single executable to distribute is a matter of taste which I like. In your case but the problems are more. It's not just about embedding the db file alone, what about the dlls associated with it? Steps are 2:

1) Add the necessary dlls (System.Data.SQLite?) associated with your db to your project as Embedded Resource (not necessarily a Resource file) and let the system automatically resolve the assembly conflicts. Catch it here how to do it.

2) Now either add your db file to your Resources of your project (and extract it)

static void DumpDatabase()
{
    var dbFullPath = Utility.GetDbFullPath(); //your path
    if (File.Exists(dbFullPath))
        return; //whatever your logic is

    File.WriteAllBytes(dbFullPath, Properties.Resources.myDb);
}

or even better do not embed the db as such in your project but write the logic to create database in your application. What if tomorrow you need to change the version of SQLite, say from 3 to 4? With the first approach you need to create a database for yourself and re-embed it in the project. But if you are writing the logic to create the db in your application then updating SQLite version is just a matter of changing the ADO.NET dll (the code remains the same). May be like this:

static void DumpDatabase()
{
    var dbFullPath = Utility.GetDbFullPath();
    if (File.Exists(dbFullPath))
        return; //whatever your logic is

    CreateDb(dbFullPath);
}

static void Create(string dbFullPath)
{
    SQLiteConnection.CreateFile(dbFullPath);

    string query = @"

    CREATE TABLE [haha] (.............)
    CREATE TABLE ..............";

    Execute(query);
}

And in the connection string add FailIfMissing=False;

If you're on NTFS, you can use an alternate data stream. On my project we hide the SQLite database inside another file using an alternate stream called :DB.

I don't think storing data in DLL is a good idea, but there is a dirty way to do it.

To load data from DLL:

1. Use System.Reflection.Assembly to load a string from DLL file. (The string is dump of DB)
2. Create empty SQLite DB in memory.
3. Use the loaded string as a query to DB to restore its content.

Now you can make any queries in memory.

To save data to DLL:

1. Dump DB content into a string.
2. Create temporary file containing SQL-dump wrapped in C# code.
3. Compile it using "csc" (or "gmcs" in Mono).

It's stupid, but it should work. Hope you will never code that way.