Is it permissible to request a fictitious employment certificate from a company—merely to prove employment to official bodies—knowing that the work mentioned in the certificate is the same private work that the person performs?

Lying is forbidden, except out of necessity or for a recognized benefit that cannot be achieved without lying, and on condition that it does not result in harm to others. If there is another way to obtain the experience certificate without lying, then it is not permissible to request it, as it involves lying and forgery. Otherwise, it is permissible, if it does not result in harm to anyone.