I went to painstaking effort to gather all this information for myself and thought everyone else would find it helpful. After the multitude of failed updates to 12.0.0 and a miserable conversation with Microsoft Support for Mac who refused to respond
to an invalid signature which they could fix: but wouldn't offer. Only that I should either buy Microsoft Office 2011 or 2016. Of course they want my money.
There are regulations about invalid signatures imposed by the FTC and Microsoft should really be reported to the Attorney General.
Here are the steps I took and I was able to get past all the **** and update all the way to 12.3.6 which is as far as you can go. I was told that Office 2008 would be 'unstable' in El Capitan OS 10.11
Hope you find this useful:
Master Link for all updates:
https://support.microsoft.com/en-us/search?query=Office%202008%20Updates&p=
1).
Office 2008 for Mac 12.0.1 Update
http://www.microsoft.com/en-us/download/details.aspx?id=6679
2).
Office 2008 for Mac Service Pack 1 (12.1.0)
http://www.microsoft.com/en-us/download/details.aspx?id=7799
NOTE: Follow these steps to execute this update otherwise you will get an error message stating the signature for this update is invalid.
a). Go to Date & Time Preferences and uncheck set date automatically and then roll back your year to 2010. Restart your Mac.
b). Disconnect your internet from your machine and/or turn off Wifi.
c). Open the Installer and run it and it will install successfully.
d). Reconnect your internet and revert the Date & Time Preferences to set Date Automatically. Restart your Mac
3).
Office 2008 for Mac 12.1.1 Update
http://www.microsoft.com/en-pk/download/details.aspx?id=21983
4).
Office 2008 for Mac 12.1.2 Update
http://www.microsoft.com/en-us/download/details.aspx?id=23198
5).
Office 2008 for Mac 12.1.3 Update
http://www.microsoft.com/en-us/download/confirmation.aspx?id=21851
6).
Office 2008 for Mac 12.1.4 update
http://www.microsoft.com/en-us/download/details.aspx?id=14172
7). Office 2008 for Mac 12.1.5 Update
http://www.microsoft.com/en-us/download/details.aspx?id=2535
8).
Office 2008 for Mac 12.1.6 Update
http://www.microsoft.com/en-us/download/details.aspx?id=9578
9).
Office 2008 for Mac 12.1.7 Update
http://www.microsoft.com/en-us/download/details.aspx?id=7597
10).
Office 2008 for Mac 12.1.8 Update
N/A
11). Office 2008 for Mac 12.1.9 Update
http://www.microsoft.com/en-us/download/details.aspx?id=22872
12). Office 2008 for Mac 12.2.0 Update
https://support.microsoft.com/en-us/kb/973254
13). Office 2008 for Mac Service Pack 2 (12.2.0)
http://www.microsoft.com/en-us/download/details.aspx?id=17575
14).
Office 2008 for Mac 12.2.1 Update
http://www.microsoft.com/en-us/download/details.aspx?id=8763
15). Office 2008 for Mac 12.2.2 Update
N/A
16). Office 2008 for Mac 12.2.3 Update
http://www.microsoft.com/en-us/download/details.aspx?id=10578
17). Office 2008 for Mac 12.2.4 Update
http://www.microsoft.com/en-us/download/details.aspx?id=7938
18).
Office 2008 for Mac 12.2.5 Update
http://www.microsoft.com/en-us/download/details.aspx?id=35602
20). Office 2008 for Mac 12.2.6 Update
http://www.microsoft.com/en-us/download/details.aspx?id=36897
21). Office 2008 for Mac 12.2.7 Update
http://www.microsoft.com/en-us/download/details.aspx?id=2889
22).
Office 2008 for Mac 12.2.8 Update
http://www.microsoft.com/en-us/download/details.aspx?id=5611
23). Office 2008 for Mac 12.2.9 Update
http://www.microsoft.com/en-us/download/details.aspx?id=4150
24). Office 2008 for Mac 12.3.0 Update
http://www.microsoft.com/en-us/download/details.aspx?id=26353
25). Office 2008 for Mac 12.3.1 Update
http://www.microsoft.com/en-us/download/details.aspx?id=27332
26). Office 2008 for Mac 12.3.2 Update
http://www.microsoft.com/en-us/download/details.aspx?id=28400
27). Office 2008 for Mac 12.3.3 Update
http://www.microsoft.com/en-us/download/details.aspx?id=29723
28). Office 2008 for Mac 12.3.4 Update
https://www.microsoft.com/en-us/download/details.aspx?id=34692
29). Office 2008 for Mac 12.3.5 Update
https://www.microsoft.com/en-us/download/details.aspx?id=35602
30). Office 2008 for Mac 12.3.6 Update
https://www.microsoft.com/en-us/download/details.aspx?id=36897
BTW, there will be no "12.3.7, 12.3.8, 12.3.9...". Support for Office 2008 officially ended in April of 2010
http://answers.microsoft.com/en-us/mac/forum/macoffice2008-macword/automatic-indentation-of-new-paragraphs-keeps-re/dbd477dc-e206-4a79-b99c-aa66addc4d46?auth=1
Vincent
http://www.microsoft.com/en-us/download/confirmation.aspx?id=17575