I asked staff at the Apple Store the same question, who consulted with a Genius. As of Mountain Lion, it is still not possible to go into Time Machine via iCal/Calendar. In other words, the only solution is to manually restore deleted entries from raw iCal/Calendar files (located in ~/Library) using Time Machine.
There is a related discussion on Apple Support Communities:
The person I spoke to also reminded me to turn off iCloud before attempting the restore procedure, as it may corrupt existing calendars.
To be able to view invisible files…
Late edit
Since Sierra (macOS 10.12) you can use shift ⇧ cmd ⌘ . to toggle visibility. You only need the old AppleShowAllFiles trick if you want to make the change permanent.
Open Applescript Editor, in Applications > Utilities then copy/paste this to a new script...
Since El Capitan the trick of changing view no longer works, so it's back to quitting the Finder
For a method to make this into a Service with key command see
https://apple.stackexchange.com/a/258741/85275
set newHiddenVisiblesState to "YES"
try
set oldHiddenVisiblesState to do shell script "defaults read com.apple.finder AppleShowAllFiles"
if oldHiddenVisiblesState is in {"1", "YES"} then
set newHiddenVisiblesState to "NO"
end if
end try
do shell script "defaults write com.apple.finder AppleShowAllFiles " & newHiddenVisiblesState
do shell script "killall Finder"
return input
Mavericks/Yosemite ought to work with this view refresh version, which was faster & smoother, but it just stopped working at El Capitan...
set newHiddenVisiblesState to "YES"
try
set oldHiddenVisiblesState to do shell script "defaults read com.apple.finder AppleShowAllFiles"
if oldHiddenVisiblesState is in {"1", "YES"} then
set newHiddenVisiblesState to "NO"
end if
end try
do shell script "defaults write com.apple.finder AppleShowAllFiles " & newHiddenVisiblesState
tell application "Finder"
set theWindows to every Finder window
repeat with i from 1 to number of items in theWindows
set this_item to item i of theWindows
set theView to current view of this_item
if theView is list view then
set current view of this_item to icon view
else
set current view of this_item to list view
end if
set current view of this_item to theView
end repeat
end tell
Then Save as an application, which you can then just double-click to toggle showing/hiding invisible files.
You don't need to kill the Finder for this toggle, a refresh is sufficient - & may be faster.
Best Answer
You should be able to restore the PDF from the backup using the command-line technique I posted in How can I restore iBooks stored in iCloud from a Time Machine backup?
Find the most appropriate backup:
Check if your missing PDF is available:
This assumes you know the name of the file, but if not you can omit the
file.pdfand you'll get the full listing for the directory.Restore the file to your Desktop:
Then you can add the PDF to iBooks again as normal.