Hi,
It's difficult to implement it, but you can follow solution:
1. Using PHPMyAdmin to export all DB tables in site Joomla 2.5 with prefix #__edocman to .SQL file
2. Open .SQL file and replace the db prefix (of site Joomla 2.5) by db prefix of site Joomla 3.x
3. Import .SQL file into database of Joomla 3.x
4. Install Edocman into site Joomla 3.x
Good luck
Dam