The webcast on this page shows how to quickly make from scanned sheetmusic small and nice looking PDF files, which fit exactly on a4 formatted pages.
Scan Tailor can save a lot of time by cleaning and straightening scanned images from sheetmusic. Unfortunately it doesn't generate PDF files, nor does it reduce image sizes if they exceed a4 pages. The second application deals with these missing features: it checks all images for orientation and size. If one or more images doesn't fit on an a4 page it will resize all images subsequently to make them fit.
Instead of supplying tiff images to the program, it is also accepts one or more PDF files. These files will be processed in the same way as for tiff images. All pages in a PDF file will be analyzed for orientation and size and if necessary resized.
What makes the second program special is that it takes a lot effort to keep a high quality of your original file. Images are stored in a lossless format for PDF (black & white, g4 encoding, average 50 kb per page.) and can be edited/annotated numerous times without losing any detail.
Further information and source code from MakePDF can be found here: http://www.auditeon.com/software:pdfprocessing