When a PDF file is created does it automatically have a the same modified date as the created date?

I was sent a PDF with a forged signature a year ago. I can see that the file was created four months before it was sent and that it was modified just minutes before they sent me the file last year. One year later, I requested the same file as a test and the content seems the same, and bears the forged signature, yet in the new file the created date and time are the same as last years file, however, the modified date and time are exacty the same as the created time stamp. I understand how it is possible to change modified and created time stamps. My question is when a PDF file is created does Acrobat automatically assign the same modified data as the created date? Is it possible for a document to be created and modified at the same exact time? Thank you!