I have thousands of PDF files in my computers which names are from a0001.pdf to a3621.pdf, and inside of each there is a title; e.g. \"aluminum carbona
You can look at only the metadata using a ghostscript tool pdf_info.ps. It used to ship with ghostscript but is still available at https://r-forge.r-project.org/scm/viewvc.php/pkg/inst/ghostscript/pdf_info.ps?view=markup&root=tm