Those files can still be recovered until certain period of time, but not when you formatted (hard reset) your phone.
Formatting or performing a factory reset is not a reliable way of permanently deleting data. Both of these things simply delete the pointers to your the data, telling your phone or other device that these sectors are now free to be used for other purposes. But unless you actually write something else to these sectors, the data on them is not deleted and can be recovered, even after a hard reset. This is the basis behind the specialized apps that BitMaxz mentions above - to actually overwrite all your sensitive data in these sectors with junk data, meaning it cannot be recovered.
I have used my phone to store sensitive information like in PDF format or TXT files that consist of recovery seeds
Why would you ever do this? Seed phrases should be stored offline using pen and paper. If you must store them electronically, then they should be stored encrypted on airgapped devices. Storing them in plain text on a phone is a recipe for disaster, even worse if your phone then automatically backs them up to the cloud or similar.