Deleting Layers in PDF files should be straightforward, unfortunately not. The user has to create another file to do this with the layer in question.
But some PDF's are locked down. This workaround breaks the security down.
Windows (not tried on a Mac)
"If you try to use Adobe's PDF printer driver, it will detect that you
are attempting to export a secured PDF to a fresh file and it will
refuse to continue. Even third-party PDF print drivers tend to choke
on such files. However, by using the XPS Document Writer, you
effectively circumvent that check entirely"
The unwanted layers always reappear after flattening / merging / saving As, even when you hide them.
Here's what worked:
1) HIDE the layers you want to KEEP. (The layers you want to delete remain visible).
2) Select Tools > Advanced Editing > Touch-up Text Tool.
3) Hit Ctrl-A to select all visible text objects.
4) Hit Delete.
5) Select Tools > Advanced Editing > Touch-up Object Tool.
6) Hit Ctrl-A to select all visible objects.
7) Hit Delete.
8) Now, you want to "merge away" the unwanted layers, which are now empty. In the Layers pane, Click the "Options" pull-down and select "Merge Layers...".
9) Hold down CONTROL and click all the UNWANTED (empty) layers.
10) Click "Add".
11) In the right-hand pane (target layer), select the first layer that you want to KEEP. This will basically merge that layer with all the empty ones, and in effect, delete the empty layers.
12) Hit OK, and you're done. When you save the file, the layers you want to preserve are preserved, and the file size is smaller, reflecting the "deleted" layers.
Technically not a GIS-SE question but is geo-image related.