  At LHCb, proton parton distribution functions (PDFs) can be studied in a
unique phase space complementary to that accessible by ATLAS and CMS,
corresponding to low and high values of Bjorken-$x$. The measurements of vector
boson production in the forward region, with and without an associated jet, are
presented. These measurements can be used to constrain the proton PDFs, and in
particular, the production of a $Z$ boson in association with a $c$-jet can be
studied to measure the intrinsic charm content of the proton.
