Convert All Text in Text File to Lowercase

Simple. Use one of the below commands: (I prefer dd)

inputfile = file to be converted
outputfile = filename after conversion

Using dd:
dd if=inputfile of=outputfile conv=lcase

Using tr:
tr '[:upper:]' '[:lower:]' < inputfile > outputfile

Using awk:
awk '{ print tolower($0) }' inputfile > outputfile