Here is a script by crgreen, crg_Text_from_File.jsx , that puts a text file into a layer (check the box when the script runs to make all one layer):
https://www.crgreen.com/aescripts/
Put the jsx file into your AE Scripts folder, then in your Comp, go File>Run Script>crg_Text_from_File.jsx
Note this only work on a text file (.txt). This creates a new layer with your text.
For the scroll, Position you layers initially, then add this expression (credit Dan Ebberts) to the Position property of the layer (this scroll works with any layer):
currentFrame = timeToFrames();
value – [currentFrame*4.0,0]
The 4.0 in line two is the pixels per frame of scrolling. You could link this to a slider if you want a little more flexibility. Otherwise change the number until you like the scroll speed.
The only hang up is that the AE text seems to only hold up to about 1300 characters then the layer gets twitchy (maybe someone more text savvy can make it visible, it’s still there just hidden in a tiny text box I think).
So 1300 characters at 4 pixels per frame is about 4 minutes of scrolling text. That’s the most I could tweak out of AE. A slower scroll rate, say 2.0 would give you 8 minutes.
But if you like the 4.0 scroll rate, a new 4 minutes scroll with different text you’d need a new layer and run the script on a new text file.
Note, if you don’t mind repeating the same 4 minute scroll, you can Animation>Keyframe Assistant>Convert Expression to keyframes, then go to the last keyframe where the scroll stops (4 minutes), select Following keyframes (available on Right Click), delete them then add this loop expression to the position property:
loopOut(type = “cycle”, numKeyframes = 0)
This will loop the 4 minutes scroll for as long as you layer or comp is. Or you could render the layer and loop when you import and Interpret Footage.