Someone asked me to convert pdf 1.1 to 1.4, I googled around, and found this:
http://stackoverflow.com/questions/3450616/convert-pdf-from-version-1-1-to-1-4-or-higher
Pdf 1.1 is forward compatible with pdf 1.4. Everything in pdf 1.1 will work with pdf 1.4 – it’s guaranteed by the spec. Let’s assume that you’ve got some justifiable reason why this is not good enough for you (let’s assume, for example, that you have a non-spec compliant tool that consumes PDF and explodes on any file version less that 1.4).
So there is no reason to convert it.
But just in case someone really need it, the following may help.
apt-get install ghostscript # on debian based system
gs \
-sDEVICE=pdfwrite \
-dCompatibilityLevel=1.4 \
-o output.pdf \
input.pdf
