you need to figure out how your simulator can write text data to a file (I have never used LTSpice so I cannot help you here) then you can use matlab to read the text file in and create a data vector that will be processed by an fft function to give you the adc output spectrum.
Once you have the spectrum, you can calculate the SNR, THD, SFDR, and so forth...
The learning curve might be a little steep but knowing the basics is fundamental in circuit design...