How can I find out the presets for my documents?

You can't know the exact presets that were used, as they are mostly parameters to create the document. You need to guess, from some indications in the PDF file, what presets could have been used. The presets are modifiable, and I used to create presets for our needs, based on existing presets. If you analysed the documents created with those presets, you would basically conclude that we used the PDF/X-4:2008, even if that was not necessarily true.

What kind of "presets", exactly?