Hi,
if the creator of the PDF had the setting to export layer information active, then you have the first step solved.
You can then start command _PDFIMPORT and inside the import settings you can activate "PDF-Layer" to import the geometry onto these layers.

But there is a general difference between how PDF is working with layers and how AutoCAD is working with layers.
One sample is a block.
While in AutoCAD a block can have geometry on multiple layers a PDF does not have such a hierarchy like "block" and so you can't get the same structure back from a PDF like the creator of the DWG-file had.
Same is happening for vertical products like AutoCAD Architecture, -Mechanical, MEP, Map3D, Civil3D as these contain custom objects which you never get back as such geometry objects.
At least and maybe most important: PDF does not work based on double precision with coordinates, so whatever you exported to a PDF is saved like "pixel coordinates on paper", but not in the same accuracy as inside the DWG-file. A line with length of 1000.001 in the original drawing could result in 999.87 after saving to PDF and then importing the PDF to dwg.
Main sentence for this: PDF is not a CAD data exchange format, it was never meant so and I would say it will not be, at least for a long time. To different is the structure.
- alfred -
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Alfred NESWADBA
ISH-Solutions GmbH / Ingenieur Studio HOLLAUS
www.ish-solutions.at ...
blog.ish-solutions.at ...
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CDay 2025------------------------------------------------------------------------------------
(not an Autodesk consultant)