You can achieve the conversion of plain text URL to hyperlinks by following these suggestions.

1. Turn on AutoFormat as You Type: Go to File > Options, Select Proofing and the click on AutoCorrect Options, Go to the AutoFormat as You Type tab then chekc the box labeled Internet and network paths with hyperlinks
2. Use Find and Replace: Press Crtl+H to opne FInd and replace, then in the Find What type the Url you are wanting to replace and in the Replace with enter the same URL again. Then finally click Replace All