Documents list that we require to connect two companies pensions at one place?

My father retired last year from his job 30 April 2017.
Till now his pension is not started.
Issue : My father worked 18 years with one company and 17 years with other total tenure 35 years.
Now what should we do to get both companies pensions in single place.
Please share documents list that we require to connect both companies pensions at one place.
Looking forward for your positive response.

You have to contact the local PF office for help while there may not be much of a problem in sorting out the pension with respect to the latter part of service, to trace out the particulars after 17 years is not an easy task. But if the pension no. is same then the task is rendered easier.