Keynote document can't be opened although its size shows normally and how to repair it?
Try this:

Rename a copy of one of the broken presentation to have an .zip extension:
Bad_Presentation copy.key > Bad_Presentation copy.zip.

Then right-click on Bad_Presentation copy.zip and choose Archive Utility from the Open With> command. This will unpack the presentation into a folder named Bad_Presentation. Take this folder, give it a new name, (Bad_Presentation_Fix) then right-click and Compress the folder back to a .zip formatted file. Lastly, rename the resultant .zip file Bad_Presentation_Fix.key. See if you can open this in Keynote.

iWork documents are not what they seem. They are actually a set of bundled resources in a folder that looks like a single document in the Finder. Sometimes the bundle format can be messed up when transferring iWork documents into and out of file systems which cannot handle this format.

Good luck!