Here is a solution for GUI to produce PDFs from Scanned documents

Only two clicks are required to scan several pages and then save all or a selection as a PDF or DjVu file, including metadata if required.

gscan2pdf can control regular or sheet-fed (ADF) scanners with SANE via scanimage or scanadf, and can scan multiple pages at once. It presents a thumbnail view of scanned pages, and permits simple operations such as rotating and deleting pages.

PDF conversion is done by PDF::API2.
The resulting document may be saved as a PDF, DjVu, multipage TIFF file, or single page image file.