gscan2pdf is a simple but a very efficient GUI to scan documents of multiple pages and convert them into PDFs or DjVu format. You can also import images from image files into PDF files and vice versa. gscan2pdf only takes two clicks are required to scan several pages and then save all or a selection as a PDF file, including metadata if required.
Scanning is handled with SANE via scanimage. PDF conversion is done by PDF::API2. TIFF export is handled by libtiff (faster and smaller memory footprint for multipage files).