Is here some tools to merge PDFs with layers?
Tried to merge PDFs with layers with pdftk, fpdf/fpdi, Gswin32c. In any cases output PDF was as simple PDF without layers.
Thanks.
Edit. I am looking for tool suitable for use it in PHP project (PHP classes or executables such as pdftk)
If you mean Optional Content (section 8.11 of ISO3200-1:2008): AFAIK no free one. There's an unmaintained fork of pdfTeX that has basic support for this, though.
You could try Adobe Acrobat or InDesign.