The PTC file format is created by PTC Pro/Engineer. I have never heard of a machine shop being so specific on the type of file format to provide when it's not DWG or STP.
Personally, I would suggest looking for a different manufacturer if they cannot handle DWG or STP.
TC Pro Platinum 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1