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Process Builder and Flow Execution Mode
Process Builder like Workflows runs in the System Mode hence not restricted by Field Level Security or object level permissions
Flows run in User Mode, Flows when Launched using a Process builder will run in the System mode.
Flows run in User Mode, Flows when Launched using a Process builder will run in the System mode.
for more detials:
However, if a Process is launching a Flow (which runs in system mode), the whole automation will run in the system mode.