An architect, an engineer or a fabricator sends you a PDF straight out of AutoCAD. You need it in Illustrator: for a sign, an exhibition wall, a presentation board, a wayfinding panel, a printed plan. In AutoCAD the drawing had thirty layers. In Illustrator it opens as one, and every wall, dimension, hatch and label is welded into the same object.
The layers are almost certainly still in the PDF. AutoCAD is one of the few applications that writes them out reliably. Illustrator just does not read them.
What AutoCAD puts in the PDF
When a DWG is exported or plotted to PDF, AutoCAD can write each drawing layer as a PDF layer. The setting is “Include layer information” in the PDF export and plot options, and it is on by default in most of the standard PDF presets. The result is a PDF where every AutoCAD layer becomes an optional content group, or OCG, with the original layer name: A-WALL, A-DOOR, A-ANNO-DIMS, E-LITE, whatever the office standard was.
Open one of these PDFs in Acrobat and show the Layers panel. You will see the whole layer list from the drawing, and you can toggle each one on and off exactly as you could in AutoCAD. The structure survived the export.
What Illustrator does with it
Illustrator does not import OCGs as layers. It has no setting for it. When it opens a PDF that was not saved by Illustrator itself, it uses a generic PDF importer that draws every visible object onto one layer in page order and drops the group tags.
So a thirty-layer AutoCAD PDF becomes a one-layer Illustrator document with several thousand paths on it. Selecting all the walls, or all the dimensions, or just the furniture, means hunting through those paths by hand, or by colour if the office used distinct colours per layer, which is not something you can count on.
The check that decides everything
Before doing anything else, confirm the layers are actually in the file. Open it in Acrobat, go to View, then Show/Hide, then Side Panels, then Layers. If you see the AutoCAD layer names, toggle a few and watch the drawing change. That is your evidence.
If the panel is empty, the PDF was made with layer information turned off, or it passed through a step that flattened it. In that case ask the sender to re-export with “Include layer information” enabled. It is a one-click change on their end and it saves you the whole problem.
Getting each layer into Illustrator
The way through is to read the OCGs directly and write each one out as its own PDF, keeping the page size and origin identical so the layers stack back in register.
Upload the AutoCAD PDF to PDFLayerExtract. The free check lists every group it finds, using the AutoCAD layer names. A large drawing may show dozens; that is normal. Once you have confirmed the list matches what you saw in Acrobat, the paid package returns one PDF per layer and a small Illustrator script.
In Illustrator, go to File, then Scripts, then Other Script, and run import-to-illustrator.jsx. It opens each layer PDF and places it on its own named layer in a single document. You now have A-WALL on one layer, A-ANNO-DIMS on another, E-LITE on a third, and you can hide the dimensions, restyle the walls and delete the electrical in seconds instead of hours.
Things specific to CAD files
AutoCAD PDFs behave a little differently from packaging PDFs, and a few points are worth knowing.
Line weights come across as stroke widths, scaled to the plot. If the plan was plotted at 1:100, a 0.25 mm pen is a 0.25 mm stroke in Illustrator. Scale the document, not the strokes, if you need it larger.
Hatches usually arrive as many small paths rather than one filled object. That is how AutoCAD draws them, and extraction keeps them as drawn. Selecting the hatch layer and applying a single fill in Illustrator is usually the quickest cleanup.
Text may be live or outlined depending on the export settings and fonts used. SHX fonts are typically outlined; TrueType fonts often remain editable text. Check before you assume you can retype anything.
Layers that were frozen or off in AutoCAD at export time are generally not written to the PDF at all. If something is missing from the group list, it was probably hidden at export, and the sender needs to turn it on and re-export.
What this does not do
It does not convert PDF back to DWG. If you need a CAD file, ask for the DWG. It does not restore blocks, xrefs, layer states or any of AutoCAD’s own structure beyond the layer separation, because none of that is in the PDF. What it gives you is the drawing, separated by layer, at the correct scale and position, in a form Illustrator can actually work with.
For sign, exhibition and print work from CAD sources, that is nearly always the part that was costing the time.