I couldn't find the handbook for Quartus version 12.0, 12.1 or any other previous version on your site.
Could you help to find them? Appreciate.
Any reason that you need old handbook? We remove old version of handbook as it's obsolete. What device that you were using? Can you upgrade to the latest release of Quartus Prime?
Chiming in here ... for certain of your legacy parts (like CycloneII series, or EPM7000 series) you have to use Quartus 13.0sp1 or earlier.
The latest Quartus DOES NOT SUPPORT these parts.
If you offer a version of Quartus for download, it SHOULD include the documentation for that version IN THE DOWNLOAD along with the binaries.
This is an issue I have had with Altera/Intel for ages and you have never addressed it.
I manage to get the quartus handbook from the Intel Link. You may refer to https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/qts/archives/quartusii_h...
Seems like we did have the handbook in the download center https://www.intel.com/content/www/us/en/programmable/downloads/software/quartus-ii-se/121sp1.html
But, when opened it, it is broken. I will let our IT to check on this.