When you teach the spell check new words, they are added to your user dictionary. You can edit this dictionary at any time, for example, to delete incorrect entries.
To do so, click on the small arrow of the icon Spell check 
on the ribbon tab Slide show | group Review and select Edit user dictionaries from the dropdown menu. The program displays a dialog box with the following buttons and options:
▪Language
| There is a separate user dictionary for each language. You can select the user dictionary to be edited from the dropdown list Language. |
Note: Note that there are two entries for each German in this list: "German (Germany)" stands for the new spelling and "German (Germany, old)" for the old spelling. The same applies to "German (Austria)" and "German (Switzerland)".
▪Entries
| This list contains all words that have been added to your user dictionary (for the selected language). |
▪"Close" button
| This option closes the dialog box. |
▪"Add" button
| This button enables you to manually add a word to your user dictionary. To do so, type the desired word into the dialog box that appears after you press this button. |
| Words added in this way are treated exactly the same as words that were added using the Add button in the spell check. |
▪"Change" button
| Use this button to edit the word that is currently selected in the list. This is useful for misspelled words that you have added to your user dictionary accidentally. By clicking on the button, you open a dialog box where you can correct the spelling of the word. |
▪"Delete" button
| This button deletes the word currently selected in the list from your user dictionary. |
| The spell check will therefore regard this word as misspelled again in the future. |