Pulling out the nib is only possible with a friction-fit nib and feed. Most modern pens (with a few exceptions) do not have friction-fit nibs. "Ink reservoirs"

Pulling out the nib is only possible with a friction-fit nib and feed. Most modern pens (with a few exceptions) do not have friction-fit nibs. "Ink reservoirs" can't always be pulled out either. A cartridge converter can definitely be taken out. "Reservoir" typically refers to a rubber or silicone bladder. These are usually fixed in place by an adhesive, and need some effort to remove.