This may be easily done in two steps.
The first thing I would is to make PDF copies of the original document(s) that you need to split using the print to PDF method.
To do so, don't focus this workflow exclusively on your hardware printing device tray requirements.
You may print to PDF using "Adobe PDF" as the virtual printing device, and just select in which paper size it needs to be printed.
For instance, if you have a letter size PDF document print it to PDF in legal letter size saving it to a separate folder.
And do the same, if you have a legal size PDF document that needs to be converted to letter size saving it to another folder (or sub-folder).
Anyhow, see the link below, it describes different export methods.
However, for the context of this topic just focus on the guidance that specifically shows how to Print to PDF:
Be aware that Adobe Acrobat Pro DC is required with a paid subscription to be able to perform this type of editing.
Please see this older discussion posted by @Adorobat back in 2017:
Using the print to pdf methods that I've recommended above, the second thing I would do is to employ the "Organize Pages" tool.
Organize Pages will aid you with actually splitting a PDF into smaller separate files (or individual sets of pages):
You may also use the Acrobat Online Services to split PDF documents (although it is limited to 20 pages at a time):