Applescript add coma between list item and return as text

This script works for me, tested on MacOS Sierra and Pages Version 6.0.5

set mfolder to "Macintosh HD:Users:me:Documents:convertme:"
set destFolder to "Macintosh HD:Users:me:Documents:converted:"

tell application "Finder" to set theNames to name of files of folder mfolder

tell application "Pages"
    repeat with aName in theNames
        set theDoc to open ((mfolder & aName) as alias)
        set newFile to destFolder & (text 1 thru -7 of aName) & ".txt" -- concat destFolder and the name without the ".pages" extension 
        my makenewFile(newFile)

        export theDoc to file newFile as unformatted text
        close theDoc
    end repeat
end tell

on makenewFile(thePath)
    close access (open for access thePath)
    -- delay 0.5 -- use the delay command, If you still have a permission issue,  increase the number of seconds
end makenewFile

Here's another method with a Cocoa-AppleScript applet, this script create the RTF file with the methods from the Objective-C code.

-- Cocoa-AppleScript
use framework "Foundation"
use scripting additions
repeat
    set customFilename to the text returned of (display dialog "Save as:" with title "Do you want to create a new, blank TextEdit RTF document?" default answer "")
    if customFilename is "" then
        beep
        display alert "The filename cannot be empty!" message "Please enter a name to continue..."
    else
        exit repeat
    end if
end repeat
set theCustomRichTextFilePathname to ((path to desktop as string) & customFilename & ".rtf")

tell application "Finder" to set b to exists file theCustomRichTextFilePathname
tell current application
    try
        if b then
            display dialog "The file \"" & POSIX path of theCustomRichTextFilePathname & "\" already exists!" & return & return & "Do you want to overwrite the file?" buttons {"No", "Yes"} default button 1 with title "File Already Exists..." with icon caution
            if the button returned of result is "No" then
                --  # The file already exists, chose not to overwrite it, just open the document.
                my openDocument(theCustomRichTextFilePathname)
                return
            end if
        end if
        -- else, the file already exists, chose to overwrite it or the file does not already exist
        my createCustomRTFDocument(theCustomRichTextFilePathname)
    on error eStr number eNum
        activate
        display dialog eStr & " number " & eNum buttons {"OK"} default button 1 with icon caution
        return
    end try
end tell

on openDocument(f)
    tell application "TextEdit"
        set theDoc to open file f
        set bounds of (first window whose its document is theDoc) to {160, 22, 883, 639}
        activate
    end tell
    tell application "System Events" to key code 125 using command down --put the blinking cursor at the end of the document
end openDocument

on createCustomRTFDocument(f)
    set myText to return & (the clipboard as string) -- Concatenation of an empty line and the text in the clipboard
    set theFile to POSIX path of f
    tell current application
        set myFont to its (NSFont's fontWithName:"Helvetica" |size|:18) -- font and size of the rtf document
        set myColor to its (NSColor's blackColor()) -- color of the text of the rtf document
        set theDict to its (NSDictionary's alloc()'s initWithObjectsAndKeys_(myColor, its NSForegroundColorAttributeName, myFont, its NSFontAttributeName, missing value))
        set AttrString to its ((NSAttributedString's alloc)'s initWithString:myText attributes:theDict) -- create an attributed string
        set rtfData to AttrString's RTFFromRange:{0, AttrString's |length|()} documentAttributes:{NSRTFTextDocumentType:(its NSDocumentTypeDocumentAttribute)} -- create the data from an attributed string
    end tell
    rtfData's writeToFile:theFile atomically:true -- write the data to the RTF file
    if the result then my openDocument(f) -- open the file 
end createCustomRTFDocument