Configure the option "Use background spell-checking" (Tools > Options)

Here you can configure if Presentations checks the spelling by marking errors with a red underline.

Supported on: At least Windows Vista
Registry HiveHKEY_LOCAL_MACHINE or HKEY_CURRENT_USER
Registry PathSOFTWARE\Policies\SoftMaker\Presentations 2016
Value NameBkgndCorrection
Value TypeREG_DWORD
Enabled Value1
Disabled Value0

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