You use form 119 to request your Principal to issue Service Certificate in event of Completion of articles, which is form 108. Form 108 is the proof of your completion, as it has the Principal's sign.. Form 119 is just an application and serves as no proof whatsoever for the purpose of completion. Form 108 is the articleship completion certificate.
Form 108 is enough unless otherwise your Principal insists on thorough paper-work, though form 108 suffices.
In general one would fill form 119 if there is any issue to obtain form 108 signed by the Principal. In that case, the articled assistant would send form 119 vide registered acknowledgement and a copy is sent to The Secretary, ICAI, Delhi. The Institute will send a letter to the Principal and if the Principal fails to respond within 3 months of completion + 15 days, it will be deemed that the details supplied by the articled assistant is correct and the date mentioned hy him/ her is correct.
If your articleship ends before February 28 (last date for exam form submission), fill and send form 108 first, then select the options which say your eligibility is based on: articleship completed else, select the provisional basis.