While there are some packages for Linux with which you can scan a document, they sometimes don't work, are buggy, require obscure dependencies, aren't available in the AUR or simply aren't free.
Some applications with which you can scan documents using Linux are:
Simplescan (doesn't work with many scanners)
Vuescan (isn't free)
Scan2pdf (requires obscure dependencies, is buggy and complicated to get to work properly)
Skanlite (many scanners don't work out of the box with Skanlite, because they are commented out in /etc/sane.d/dll.conf)
If none of those packages work for you due the above-mentioned reasons, then there is a very good option that probably will work, is free and easy to use, namely scanning documents using GIMP and the xsane-gimp package.
Follow these steps in order to be able to scan documents using GIMP and Xsane.
1. Install GIMP
2. Install the xsane-gimp package
3. Open GIMP and click: File > Create > Xsane:yourscanner
4. Now change the scanmode from 'Lineart' to 'Color'
5. Change the scan resolution from 75 to 300 DPI
6. Press the scan button
7. Save the image using GIMP
Voila. There you have a free way to scan documents into GIMP. The great thing about it is that you can immediately edit the document and save the edited version.
That's it. Enjoy.
Note: xsane is also available as a standalone application/package.