Scott
It was indeed necessary to have such a certificate of good behaviour, - often called a testificate, - but it's very rare for them to survive, - I'm very fortunate to have one from 1804. Such a testificate was required before he could join a congregation in his new location, - Perth if he was living and worshipping there.
You may or may not find mention of new communicants from other areas who have joined the church after moving into the area from elsewhere, but you will be totally in the hands of the session clerk as to the level of, detail, if indeed there is any apart from his name, that is included in the kirk session minutes.
And then you have the not inconsiderable problem of knowing which of the congregations in Perth, both established and secession, that he may or may not have joined
Sessional records take the form of large books with minutes of the meetings of the session, sometimes very detailed, but sometimes very short, e.g. "This day the Session met" !, along with, sometimes, sets of church accounts, records of use of the mortcloth, and, sometimes baptismal and marriage/banns records whoch really should have gone in the OPR but sometimes got mixed up.
Most extant sessional records are at NAS in Edinburgh, but there is a small number of such records at various local archives, sometimes duplicated at NAS, sometimes not. See the above post re the digitisation project.
David