I am unsure, but I think the ACSM is an Adobe Editions file that probably contains protected material, hence unlikely to be converted into a pdf file.
Unfortunately the answer you got from Michael is incorrect.
.ascm files are created when you start the downloading process from a
website - a publisher, distributor, author or library. .ascm files are not
ebooks. They are a pointer or 'tag file' that tells Adobe Digital Editions
(ADE) where to find the ebook text plus some other information ADE needs to
know in order to download the ebook to your computer.
Let me assume that you tried to download an ebook (in .pdf format?) and all
you got was this .ascm file. What happened was that the place from which
you downloaded that ebook didn't tell ADE on your computer to go and get
the ebook - it just dropped this 'tag file' on your computer. What you can
do now is to find that file and tell your computer to open it with ADE. If
you're using Windows, you can do this by finding the file using a utility
program, such as Windows Explorer (NOT Internet Explorer), and then
right-clicking on the fine name. The drop-down menu will give you a choice
'Open With', and you should move your cursor to that entry. A list of
programs will be displayed. Windows might be smart enough to know that
this format is opened with ADE and give you that choice. If it doesn't,
then pick 'Adobe Digital Editions' and it will go and find the ebook and
open it for you.
Here's a reference article:
Hope this helps!