Yes, the .data folder is present. When I copied the folder with .enl files and .data folder to another computer with Endnote X1, everything works nicely.
On the computer with Endnote 9, I tried different PDF readers and “PDFwrapper” from the thread you suggested, but still cannot open PDFs from endnote.
I noticed that in Endnote 9 the icons in the attachment column (the one with paper clip) are not displayed (but the Open PDF option after right click on the reference is active). I can see this icon on another computer with Endnote X1. So I think that it is rather a problem with Endnote or library itself, rather than PDF reader.
I solved (more or less) the problem in the following way:
In Endnote X1 export the library in Endnote Export format
In any text editor search and replace the “internal-pdf://” to “file:///full_path_to_endnoteX1_PDF_folder”
In Endnote 9 import the lib as Endnote Import format.
Change the field type of the first column to “Link to PDF” ( Menu Edit → Preferencess… → Display Fields)
Things that do not work, and probably will not work:
When two PDFs has been attached, none will open after clicking “Open PDF”. There are at least two half-solutions to that, which will enable openning of the first PDF file: 1. Delete the line with the second PDF file 2. Add “%>” to the second line
The paper clip is not drawn when PDFs are attached, somehow paper clip column is reserved for Image Field.
The paths to PDFs must be absolute, I haven’t found a way to use relative links. That means that the paths must be changed for each computer (probably using Export -> Change path in editor -> Import)