I have generated a pdf file using matplotlib and I want to add a logo to this pdf file. How can I do it
If you can do it the other way round, it is easier:

plot the image
load the logo from file with, e.g. Image module (PIL)
add the logo with plt.imshow, use the extent keyword to place it correctly
save the image into PDF

(You may even want to plot the logo first, so that it stays in the background.)
Unfortunately, this does not work with vector graphics, but as logos usually are not that large, you may use a .png or even a .jpg.
If you already have the PDF's then this is not a matplotlib or python question. You need some PDF editing tools or libraries to add the logo. Possible, but an entirely different thing.
I am using matplotlib to draw a graph using some data and I have saved it in Pdf format.Now I want to add a logo to this file.How can I do this.
Thanks in advance