XMind software offers export capability to various formats (including PDF), unfortunately only in the Pro (paid version). If you do not own licence to the program, you basically have two options left for xmind to pdf conversion. Either find another mindmapping tool with support of .xmind files and export to PDF there, or try o download the 30-day trial version of Xmind - if you haven't already. It is extremely unlikely that some utility designed just to convert xmind to pdf exists.
Open XMIND file Open PDF file