There never was a formal conversion document. If you are playing 1E, use the 1E rules. If you are importing PC's into a 1E game that exceed 1E limits, reduce the PC's to those limits, or with the permission of the DM consider them to be exceptions. If you are playing 2E, use the 2E rules. If you are importing PC's into a 2E game that exceed the 2E limits, reduce the PC's to those limits, or with permission of the DM consider them to be exceptions.
If you are playing a game that mixes 1E and 2E rules (AND OD&D?) well then you're really on your own as to what converts and how. 2E intentionally retained a LOT of 1E rules only to maintain backward compatibility, although the list of TWEAKS to the game is really, really long. 2E also dropped a lot of things from 1E only to bring them back later in some form as 2E rules supplements came along.
If you're not the DM then none of it is up to you. You ask the DM of the game you're in if you'll even be permitted to import your PC's from other games and especially from other editions because THEY will have to then have their own policies or formal procedures for letting that happen. The close similarities between 1E and 2E were intended to make moving between editions and different campaigns possible - but that doesn't mean that it automatically had to be allowed for any reason. While mixing OD&D with any other edition is also possible, it was hardly ever even considered that people would want to do that - it's strictly house rule territory.
My advice to a DM would be to pick ONE edition to base your game on. Import SELECTIVE pieces from elsewhere if you must but otherwise convert everything to that chosen edition's rules and mechanics. If you choose to base your game on 1E then there are still rules that you want to change or IGNORE from that edition, not the least of which is ridiculous notions it had about different stat limits for male and female PC's. It's indefensible with modern attitudes and served no point in the first place. As for importing PLAYER characters, I'd say it rarely works out as well as anybody wants it to. Don't cling to past glories - MAKE NEW PC's and give THEM new tales of adventure and glory to remember instead.
Let PC's retire with the campaigns that made them what they were. Importing them to a new game only means changing what world they are in, what foes they have faced and WILL face, what companions they had or will have, etc. One thing I've found consistent with players trying to import their old PC's is that they only want to import the ones that already dominated the games they USED to be in, never any kind of PC that struggled before and the player wants them to have new opportunities. Nope it's always a desire to CONTINUE the outrageous amounts and power of magic items, excessive levels, histories that seldom have ANY basis in the history of the new game setting, and so on. Worst of all is if their imported PC simply doesn't live up to the player's fantasies of domination of yet another game setting because the DM doesn't want to just HAND THAT OVER without anyone having even rolled one die in THIER campaign. Make NEW PC's that don't need complicated conversions. Make NEW memories of fun gaming. Create a PC that is a product of THIS game world - not a shadow of a previous one that others at the current game table never even knew.