Do you need to modify the ModDate (Modification Date) and CreationDate fields in PDF file? if yes, VeryPDF Advanced PDF Tools software will useful to you, you can use Advanced PDF Tools to modify ModDate (Modification Date) and CreationDate fields in PDF file easily.
The first, please look at following web page to understand the date format in PDF file,
You can download and install Advanced PDF Tools software from this web page,
and then click "Change" button, you will get a new PDF file, the dates will be changed properly in the new PDF file.
This is the date in original PDF file,
This is the date in new PDF file, as you see, the date fields have been changed properly,