The parameter filespec is not expanded.
MWE:
\documentclass{article}
\newcommand{\filename}{FileName.bib}
\newcommand{\fullpath}{Test.bib}
\usepackage{intopdf}
\begin{document}
\attachandlink[\filename]{\fullpath}[application/x-bibtex]{BibTeX entry of this paper}{BibTeX}
\end{document}
PDF:

Instead of "filename", fileName.bib should be shown.
I tried with the trick \romannumeral-`X, but it did not help.
The parameter
filespecis not expanded.MWE:
PDF:
Instead of "filename",
fileName.bibshould be shown.I tried with the trick
\romannumeral-`X, but it did not help.