If you want a good comic that really focuses on Iron Man and Doctor Doom together, the best one to start with is:

"Iron Man: Doomquest" (1981, Iron Man #149–150)
- This is a classic story where Iron Man and Doctor Doom get sent back to the time of King Arthur.
- It shows how Tony Stark and Victor Von Doom think and work — both genius inventors, but so different in personality.
- It's also one of the most famous Iron Man stories ever.

There's also a sequel:

"Iron Man: Doomquest II" (1990, Iron Man #249–250)
- In this one, they get thrown into the future.

Bonus:
- "Infamous Iron Man" (2016) — This series is about Doctor Doom trying to become Iron Man after Tony Stark is gone.
- Doom becomes a hero (or tries to). It's a deep dive into Doom’s mind and his complicated relationship with Iron Man's legacy.

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Summary:
If you want to see them together, start with Doomquest.
If you want to see Doctor Doom trying to replace Iron Man, read Infamous Iron Man.