As long as you have a valid product key you should be able to search for the windows 7 ISO and download it to make a windows 7 disk. The issue is locating the the drivers. Try the acer web site and the web. I had an acer with windows 8 installed and since I had a key for windows 7 was able to download everything I needed from the internet. Last resort is to buy the restore from ACER.
DigitalRiver offers legitimate, legal, downloads of the Windows 7 ISO file. Download the correct version, 32 or 64 bit and home premium professional etc, and burn the disc and install from that. However you will have to track down and install your own device drivers - those are typically not included on the generic ISO. A tip, as I have done this myself, while installing it will ask for your product-key, put it in but do not select automatic activation. Instead install the disc and then once installed go into the control panel and choose the system applet then choose change product key and put in your same product-key as you did in the installation. If you don't do it this way then the product-key will fail to activate, however if you do and your product-key is legitimate then it will work. 153554b96e