Question: Please suggest books/references on ARDL model and ARDL bounds test approach to study.

Answer: 
A classical textbook on cointegration in the ADL/ECM framework is [Co-integration, Error Correction, and the Econometric Analysis of Non-Stationary Data](https://global.oup.com/academic/product/co-integration-error-correction-and-the-econometric-analysis-of-non-stationary-data-9780198288107?q=cointegration&lang=en&cc=fi) by Anindya Banerjee, Juan J. Dolado, John W. Galbraith, and David Hendry. Another good text is [Time-Series-Based Econometrics: Unit Roots and Co-integrations](https://global.oup.com/academic/product/time-series-based-econometrics-9780198773535?cc=fi&lang=en&) by Michio Hatanaka.
The GRETL progrmme will be more useful, if it includes the test for degeneration case 1 using ARDL Bootstrap method along with PSS and BDM bounds test on cointegration..

McNown et al. (2016) define the following degenerate cases and the degenerate cases cannot be cointegration.
1. Degenerate case #1 occurs when the F-test on joint lagged level variables and the t-test on the lagged independent variable are significant, but the t-test on the lagged level dependent variable is insignificant.

2. Degenerate case #2 occurs when the F-test on joint lagged level variables and the t-test on the lagged dependent variable are significant, but the t-test on the lagged level independent variable is insignificant.

Pesaran et al. (2001) present critical values for case #2, but not for case #1. To rule out degenerate case #1, the integration order for the dependent variable must be I (1).