use AppleScript version "2.4" — Yosemite (10.10) or later
use framework "Foundation"
use framework "AppKit"
use scripting additions

set pNum to retPreviewDispPageNumber() of me

on retPreviewDispPageNumber()
　　set aLocName to getLocalizedName("com.apple.Preview") of me
　　
　　tell application "Preview"
　　　　if (count every document) = 0 then return false
　　end tell
　　
　　tell application "System Events"
　　　　tell process aLocName
　　　　　　tell window 1
　　　　　　　　set aTitle to title
　　　　　　end tell
　　　　end tell
　　end tell
　　
　　set aPageInfo to pickUpFromToStr(aTitle, "(", ")") of me –English env
　　if aPageInfo = false then
　　　　set aPageInfo to pickUpFromToStr(aTitle, "（", "）") of me –double witdh parenthesis (Japanese env)
　　end if
　　set pList to words of aPageInfo
　　set hitF to false
　　repeat with i in pList
　　　　set nRes to chkNumeric(i) of me
　　　　if nRes = true then
　　　　　　set hitF to true
　　　　　　exit repeat
　　　　end if
　　end repeat
　　
　　if hitF = false then return
　　return i as integer
end retPreviewDispPageNumber

on getLocalizedName(aBundleID as string)
　　set pRes to getProcessByBUndleID(aBundleID) of me
　　if pRes = false then return ""
　　set pName to pRes’s localizedName()
　　return pName as string
end getLocalizedName

–指定プロセスを取得する
on getProcessByBUndleID(aBundleID)
　　set appArray to current application’s NSRunningApplication’s runningApplicationsWithBundleIdentifier:aBundleID
　　if appArray’s |count|() > 0 then
　　　　set appItem to appArray’s objectAtIndex:0
　　　　return appItem
　　else
　　　　return false
　　end if
end getProcessByBUndleID

on pickUpFromToStr(aStr as string, s1Str as string, s2Str as string)
　　set a1Offset to offset of s1Str in aStr
　　if a1Offset = 0 then return false
　　set bStr to text (a1Offset + (length of s1Str)) thru -1 of aStr
　　
　　set a2Offset to offset of s2Str in bStr
　　if a2Offset = 0 then return false
　　
　　set cStr to text 1 thru (a2Offset – (length of s2Str)) of bStr
　　
　　return cStr as string
end pickUpFromToStr

–数字のみかチェック
on chkNumeric(checkString)
　　set digitCharSet to current application’s NSCharacterSet’s characterSetWithCharactersInString:"0123456789"
　　set ret to my chkCompareString:checkString baseString:digitCharSet
　　return ret as boolean
end chkNumeric

on chkCompareString:checkString baseString:baseString
　　set aScanner to current application’s NSScanner’s localizedScannerWithString:checkString
　　aScanner’s setCharactersToBeSkipped:(missing value)
　　aScanner’s scanCharactersFromSet:baseString intoString:(missing value)
　　return (aScanner’s isAtEnd()) as boolean
end chkCompareString:baseString: