I believe you will need to accomplish this outdoors via
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knoji.com/images/user/We ··· 421.jpegThe "trick" is to install so as to stop air flow, but not so tight that closing the door creates a challenge to get door to latch. Slightly and gently leaning against door from outside while installing weather strip, with vinyl or foam edge just touching door during fastening would be a good way to go. Pressing the sealing edge in very tight will create a hard to latch door. Been there...
To add an outdoor sweep that can come into contact with newly installed weather strip wouldn't hurt either. To take a photo or two of outside of door to hardware store could be helpful if you want to shop for a sweep that will complement weather strip shape.
I would avoid methods where stripping is installed between door stile and door frame as door is old, and space between two areas is likely inconsistent. Level and plumb may be infrequent visitors as well.
Not that you asked, [as if that ever stopped me before
] but if house has a door from inside first floor to cellar stairs, that's often a good candidate for weather strip and sweep too.
ps - pardon me for being a noodge, but, while you're at the hardware store, please consider picking up a knob style deadbolt instead of a key type. Very very dangerous situation when a key is required to exit any type of structure.
Just sayin'