Size limits for JPG or JPEG files

The physical image size limit for .jpeg compression is 65,535 pixels, this applies to any file format that uses >jpeg compression.

If you need to capture an image that is too large to work with .jpeg you can instead use .tiff with deflate or G4 compression.

PDF does not have an explicit file size limit again the same rule applies since PDF uses .jpeg compression for images it will also have the physical image size unless compression is turned off.

Architecturally there is only one limit in the PDF standard: the overall file size must be below ~10GB as the cross-reference tables which define the PDF structure use 10 bits.

A workaround could be to scan at a lower resolution to say 200dpi with a file format as TIFF.  Use a different compression (or no compression),