I can't export 4500x2500mm image with 300 or even 150 dpi. Need to do it with only 96 dpi.
I'm using Acrobat X Pro.
What is the limit and why is there limit?
That combination is way too large for anything to handle, especially a 32-bit application such as Acrobat. 4500mm at 300dpi is 53150 pixels wide (giving a 1496 megapixel image).
Sounds like a job for a pro photo tool like Photoshop, but it may be too large for that. I think PSD is limited to 30,000 x 30,000 pixels.
Photoshop CS and later can work with documents up to 300,000 pixels in each dimension, but it's limited by RAM and when saving a document you have filesize limits due to the bit depth of the headers:
PSD = 2GB
PSB = 4GB
Tiff = 4GB
A Tiff file can in theory contain an image with a 4 billion pixel canvas dimension, but in practice it would exceed the filesize.