This post is for everyone who has/has not installed a custom ROM and wants to restore his HTC device's personal user dictionary in AOSP/Google or any other keyboard.
Edit: This method also works if you want to copy your stock HTC Keyboard's dictionary to another keyboard like Google Keyboard or others.
1.Backup of your user dictionary from HTC device. You must have the PersonalDictionary.htcudb file. To get this file go to Settings(on your HTC ROM), and then tap Language & keyboard >Tap HTC Sense Input.>Tap Personal dictionary >Back up to email.
When prompted, tap OK. You have the PersonalDictionary.htcudb file now.
2.Any office suite application.(MS Office 2010 Recommended)
3.User Dictionary Manager(UDM). Make sure you have it installed. You can find it on Google Play.
1. Open the PersonalDictionary.htcudb file using the Word Processor. Use encoding UTF-8.
2. You will notice all your added words separated by "|" symbol. Select all data and do Ctrl+G
3. Go to Replace tab and type "|" (without qoutes ofcourse). Click on "More" button, and then click on "Special" button. Select Manual Line Break option from the drop down menu.
4.Click on REPLACE ALL button. Wait until all words are arranged in one word per line format.
5.Save the filename as wordlist.txt. Move it to your sdcard.
6.Open the UDM application(ON your Custom ROM). Click on Import. Select "external- TXT file" option. CLick next. Wait until all words are imported to your dictionary.
If you like UDM app, please rate it. Give respect to the devs.
If you found my post helpful, please don't forget to click the THANKS button.
This method is tested on HTC One X(endeavoru) but it should work on other HTC devices too.