If you would like to convert all your 2003 office documents to 2007, but would like to do all of them in a single shot, here you go.
1. Download Migration Manager from microsoft and install it, which is a free tool
2. Download Office compatibility pack
Once step 1 is done, open the folder where it is installed and look for tools\ofc.ini
Below ofc.ini is complete file and we are interested in one part, the path to provide the source folder under [FoldersToConvert], make sure you have this fldr=C:\localfolder (without a ; before fldr and where localfolder is name of your folder)
; The Converter will attempt to convert all supported files in the specified folders
; (do not include if specifying FileListFolder)
Also you can update DestinationPathTemplate to the path where your converted files need to be available
4. Now open cm.exe and navigate to folder where migration manager is installed and simply run the cmd as ofc.exe
all your files will be converted and available in destination provided above without original files getting affected.