hehehe... you my friend are in for a fun ride...
steam version eh? me too. let's see if I can walk you through this.
On steam, right click on grand theft auto 4 in your library, then on "Properties" which should be at the very bottom, now on the new window that just opened up click on "Set launch options..." and copy and paste the following into the box that shows up:
-norestrictions -nomemrestrict -availablevidmem 4096 -reservedApp 0 -refreshrate 30 -noprecache -frameLimit 1 -windowed -reserve 0
What this is going to do for you is let you change the graphics settings, and more importantly actually play the game with less crashes and it will help you avoid the dreaded disappearing textures bug.
Next, this is almost as important as the previous step. you are going to download this thing called xliveless. it will completely disable social club. if you were planning to play online, sorry. but the chances of you actually getting the game to run ok with it are almost none. here's the link to xliveless, just drag and drop the files into your GTAIV root folder which is the one that contains GTAIV.exe https://www.moddb.com/games/grand-theft-auto-iv/downloads/xliveless-0999b7
So ya already did the paul.old.dll thing. hopefully those 2 steps above fixes whatever you said went wrong with that, if it didn't then just tell me.
Now... start up gta 4 and make sure everything is working A-ok. nevermind, gta 4 will never work A-ok, just make sure that it's playable. [:
If it's not then explain to me in great detail what's not working.
If it is working then go download lcpdfr 1.1. install it using it's installer which should install itself. (basically just double click the installer and it will walk you through the installation.
Once again after that's done start up the game again and make sure that everything works, if it does then press "ALT+P" you should get a message that lcpdfr has started up or something like that.
if that works then congratulations, you just installed everything correctly and can now play lcpdfr until your little peasant eyes melt out of their sockets from your PC screen.
Now, their is ABSOLUTLY NO WAY that you got this on the first try, so just message me back with whatever goes wrong and I'll get back to you as soon as I can when I feel like it.