pdfz is not an Adobe supported file type. I can find no reliable search for this type of file on the internet. One search seemed to indicate it might be a type of ebook. I'd recommend you contact the church for help with this.
They may just renamed the file extention so that it could not open directly in browser (force download)
You can rename the file extention (pdfz) to (pdf) and open with adobe reader.
You can also open adobe reader, drag and drop your pdfz files in it...