estimating target debt ratio

1. I am trying to find way to apply partial adjustment model. Can it work for two values lev and lag(lev) as defined in equation 3 of the attached jpeg. any explanation from other sources
would be appreciated.*
2. Is there anyway in stata which lead me to estimate equation 5 for each firm for each year. Sorry I don't know much in this regard. Previously I have learned only OLS estimation.