Why do layers do not show up in Adobe Pro?

[dutch eef]

My customer tells me that she checked the layers in a High Ress Pdf I made (Preset: PDFX 3 2002 and Acrobat 5). I tried to see these layers my self, but they do not show up in the layer panel. Can anybody help. Whatever I try, they never show up.

I am working in Acrobat Pro X. In the Preferences/Document I switched off the 'Allow layer state to be set by user information', which was a suggestion on a website, but this does not change anything. I would be very grateful if anybody is willing to help.

[Test Screen Name]

There can not, must not, be any layers. PDF/X-3 forbids them. You need to ask the customer exactly what was checked, with what software, and how. The term "layer" might be used informally in various ways.

[dutch eef]

Thank you for your answer. I did ask my customer these questions and she answered me that she could switch layers on and off Acrobat. Is it possible that there is an other way in Acrobat to show and hide layers in Acrobat, do you think? Thanks again. 

[Test Screen Name]

‌There must be no layers as I understand them (or it is not PDF/X-3; later PDF/X versions allow it). Is it possible there is an earlier working copy of the file? Or that the customer has been through another app, like Illustrator, and resaved? I recommend double checking that, then asking for a screen shot showing the list of layers.

[dutch eef]

To be honest, I do not want to ask too much, because I don't want to give the impression that I don't know what I am doing. That makes it all so difficult. No instructions from the printer nor from the customer (as usual), but at the other hand, I must admit I probably need to know more of Acrobat. Anyway, you are probably right, they seem to work in a way I did not figure out yet. Thank you for your answers!