Hi guys, I tried the "search" engine but it does not give me any results, so if I am reposting I apologize in advance(d&d).
I am not an experienced GM in D&D and I would like to know if there is or will be like a pdf with conversion guidelines. My idea would be to convert for example, an AD&D2nd Planescape module or campaign to 5ºE and if it would be like coherent.
Thank you 
There are no conversion guides yet.
Though the dev's have mentioned them several times. Possibly in the DMG.
Simple conversion before the guidelines are solidly out:
To-hit bonus = (20 - THAC0)
For example, someone with 19 THAC0 has a +1 to hit.
AC = (20 - 2eAC)
For example, someone with 6 AC in second ed, now has 14 AC in 5th ed.
This works reasonably well at low levels, but doesn't really work as well for higher levels because it doesn't fully take into account bounded accuracy. I'm not sure exactly what the conversion formula should be.
HP, Hit Dice, Damage, ability scores (when present), alignment, ecology = all same
XP, CR = look for something in 5e with a similar HP, AC, To-Hit, Damage-per-attack output (multiplied by number of attacks if applicable), and special abilities. Give it that XP and CR.
Special abilities = This is toughest because you kinda have to adjudicate it case-by-case. My best short-version recommendation is, if the special ability resembles a spell, look for the closest similar spell of the same level in 5e, and make it resemble that. For example, Dominate Person used to be notably stronger than it is. If a monster has an ability that's very similar to the 2e Dominate Person, then make it work like the 5e Dominate Person now. (I.e. requires concentration and only lasts a minute unless you cast it with a higher-level spell slot.)
Magic items = convert to weaker equivalents.
+1, +2 are now +1.
(Non-artifact) +3, +4, +5 are now +2.
Artifacts are now +3.
mellored wrote:
I remember reading something from some Wizards crew member saying that it worked almost impossibly well, just substituting monsters from 5e for their 2e counterparts. Obviously, if you're looking to use Planescapes, you are going to have a couple things that don't show up in the new Basic set or the two bestiaries (Lost Mine and Hoard), and probably not even in the MM. You can try to find a monster in 2e that is of similar power to what you're looking at that does exist in 5e and go from there.
The great thing about being the DM is that you can make stuff up if you need to -- did you make that monster a little more powerful than you thought it would be? Nerf its HPs for the encounter so that the PCs (or at least a couple of them) survive, make notes, and make changes for the next time they might run into the same thing.
I'm sure if you have a question on a power or ability that a monster has in 2e that isn't addressed on a 5e monster yet, you could post it in the DM's section and a bunch of people would help you out with suggestions to format the power for 5e. :D