I recently returned to the church after being away for many years. I bought a daily missal and would follow along with the priest at mass. I saw such beautiful prayers that the priest says that the congregation does not say. Other than the consecration portion of the liturgy, is it permissible to pray along with the priest? e.g. " May almighty God have mercy on us, forgive us our sins, and bring us to everlasting life" or “Through Him, with Him, and in Him, in the unity of the Holy Spirit, all glory and honor is yours, almighty Father, for ever and ever”.
Each person has a role in liturgy and we shouldn’t attempt to mix them together. However, quietly praying along with the celebrant is not a problem and indeed is laudable; it would only be a problem if you were praying aloud and confusing/distracting others.