A LOT...Their basic religious beliefs are based on the forgeries of Ignatius...Without those forgeries, they don't have a religion...
The Donation of Constantine...
The Isidorian Decretals (which falsely gives them the authoity for their popehood)...
And many others...
They still reference Thomas Aquinas' use of these false Decretals even knowing they have been proven forgeries...
I can’t even imagine putting my faith and trust in an organization that relies on and references proven forged documents.
And that, in the end, causes ALL of the church fathers to be suspect, especially those which are foundational (400AD and earlier). The forgeries and inclusions, by and large, are designed to bolster the Roman church's position - To create a history, a precedent. That speaks to it being institutional. purposeful. How can any of it be trusted?