HP LaserJet 4050 Printer series - Manual (Page 188)

A-8 Specifications
EN
Note Do not use letterhead paper that is printed with low-temperature
inks, such as those used in some types of thermography.
Do not use raised letterhead.
The printer uses heat and pressure to fuse toner to the paper. Make
sure that any colored paper or preprinted forms use inks that are
compatible with the printer’s temperature (400° F or 205° C for
0.1 second).
Avoid using paper that has already been used in a printer or copier.
(Do not print on both sides of envelopes, transparencies, or labels.)