First, log into your Greenhouse account. Navigate to the "Reports" section and select the data you wish to export. Use the custom report feature if necessary to tailor the data set to your needs. Export this data in a CSV format, as this will be easily ingestible by DuckDB.

Ensure that DuckDB is installed on your local machine. If it is not, download and install it from the official DuckDB website. Make sure that you have access to the command line interface of DuckDB for executing SQL commands.

Open the DuckDB client on your machine. Use the following SQL command to create a new database or open an existing one:
```sql
.open mydatabase.duckdb
```
Then, load the CSV data into a new or existing table using the following command:
```sql
COPY mytable FROM 'path/to/your/greenhouse_data.csv' WITH (FORMAT CSV, HEADER);
```
Replace `mytable` with the desired table name and update the file path accordingly.

Run a simple SQL query to verify that the data has been successfully loaded into DuckDB. For example:
```sql
SELECT COUNT(*) FROM mytable;
```
This will return the number of records in the table, allowing you to verify that the import was successful.

Depending on your needs, you may want to clean or transform the data within DuckDB. You can use standard SQL commands to perform operations like removing duplicates, filtering rows, or adding new calculated fields.

To ensure efficient query performance, consider creating indexes on frequently queried columns. Use the following command to create an index:
```sql
CREATE INDEX idx_column_name ON mytable(column_name);
```
Replace `column_name` with the column you wish to index.

It's always a good practice to back up your database after data import and transformation. You can do this by simply copying the DuckDB database file (`mydatabase.duckdb`) to a secure location.

By following these steps, you can successfully move data from Greenhouse to DuckDB without relying on third-party connectors or integrations.