@DilipanV105 In Pega, a File Data Set always adds the system name (your environment name) and a unique ID to the output file name to keep every run unique and avoid overwriting files.
That behavior is built into the File Data Set runtime, so there is no rule you can edit to stop or remove the suffix.
So you cannot produce a fixed name like CustomerDataFileExtract.csv directly from a File Data Set output.
Since there is no way to avoid the unique ID getting appended to FileName, I renamed the file after it got generated in the postActivity of the data flow using combination of D_pxListFiles, D_pxGetFile, D_pxNewFile, D_pxDeleteFile D Pages(API)