An inherited PDF is any print file you did not make and cannot get the source for. A client’s old packaging. A label from a supplier who has since changed hands. A sign layout the previous designer left behind. The job is live, the deadline is real, and all you have is the final PDF.
Illustrator opens it as one layer. Here is the sequence that gets you from that single layer to a working document, in the order that wastes the least time.
Step one: find out whether there is anything to recover
Do this before you touch Illustrator, because the answer decides everything that follows.
Open the PDF in Acrobat. Go to View, then Show/Hide, then Side Panels, then Layers. You are looking for a list of named groups: Cut, Dieline, White, Varnish, Spot, Print, Notes, or whatever the original tool called them.
Toggle each group on and off and watch the page. What you want to see is content appearing and disappearing. A cut line that vanishes when you hide “Cut” is a real, separate group. If the panel is empty, or every toggle leaves the page unchanged, the layers did not survive export, and the honest answer is that the file has to be rebuilt.
Write down what you found: page count, group names, and which groups actually changed something. That note is worth more than any amount of trial and error later.
Step two: get each group out as its own file
If the groups are there, the goal is one PDF per group, each keeping the original page size and position so they stack back together exactly.
Illustrator cannot do this itself, because it discards optional content groups on import. Acrobat can hide and show them but cannot export them as separate documents. What you need is something that reads the group structure directly and writes each group out on its own.
Upload the PDF to PDFLayerExtract. The free check lists every group it detects, sorted by type: spot, clear, cut, print and info. Compare that list with your Acrobat note. If they match, the file is a good candidate. If the check finds nothing, stop here; you have confirmed the layers are gone without paying for anything.
The paid package is a ZIP with one PDF per detected group and an Illustrator script called import-to-illustrator.jsx. The price depends on how much is in the file and is shown after the check, not before.
Step three: bring them into Illustrator as layers
Unzip the package. In Illustrator, go to File, then Scripts, then Other Script, and choose import-to-illustrator.jsx. The script opens each group PDF and places it on its own named layer in one document, in the right order, at the right position.
You now have what the original file was carrying: cut on its own layer, varnish on its own, print artwork underneath, notes on top. Lock what you do not need, recolour what you do, and send it on.
If you would rather not run a script, you can also open each PDF individually and paste in place. The script simply saves you doing that six times.
What to expect, and what not to
The result is a production separation, not a restored design file. Text that was converted to outlines before export stays as outlines. Live effects that were flattened stay flat. The designer’s original layer names, sublayers and appearance settings do not come back, because the PDF never contained them.
For most inherited print jobs, that is fine. The part that costs hours is redrawing the dieline, isolating the white underprint, or separating the varnish from the artwork. Those are exactly the groups that survive as OCGs, and exactly the groups you get back.
When the three steps do not apply
If step one shows an empty Layers panel, the file was flattened before it reached you, and there are no groups to extract. If the groups exist but every one contains the whole page, the exporting tool used layers for something other than separation, and extraction will give you duplicates rather than parts. In both cases the free check will show it, and the right move is to rebuild or ask the sender for the source.
The point of the sequence is that you find that out in step one, in Acrobat, for free, instead of discovering it three hours into a manual rebuild.