Pdfposter can be used to create a large poster by building it from multiple pages and/or printing it on large media. It expects as input a PDF file, normally printing on a single page. The output is again a PDF file, maybe containing multiple pages together building the poster. The input page will be scaled to obtain the desired size.
This is much like the well-known tool poster does for Postscript files, but working with PDF. Since sometimes poster does not like your files converted from PDF. :-) Indeed pdfposter was inspired by poster.