About two months ago I tried to find a FREE application that could scan to PDF. The only thing I found was Scan2PDF and it just didn't work. I have yet to see ANY free Windows utility that supports scanners (e.g., GIMP). Most of the low-cost "output to PDF" software available just creates a virtual printer, it does not perform scan-to-PDF. (Although most scanners on the market include scan-to-PDF software, that doesn't help companies with older scanners, e.g., "all-in-one" inkjet scan/fax/copy/printers.)
And that doesn't even consider the "Swiss Army Knife" functionality of Acrobat, e.g., secure/certified PDF's, built-in OCR, create forms, etc.
Although we have a copy of Acrobat Standard (ver 6), we generally use VERY limited functionality, mainly occasionally scanning documents to a PDF to attach to an email. I also often print to Acrobat's virtual printer, although doPDF and a number of other free utilities can provide that functionality.
I also have Nuance PDF Converter Pro, which seems to be functionally equivalent to Acrobat Standard 9 (which I have at home).
Of course, that is completely separate from replacing Photoshop, which we don't use. When I need to do graphics editing (infrequently), I use Paint Shop Pro.