how we can eliminate the Invalid multipart content type and file ending combination document ?

Have you enabled the setting in the Admin Console to validate that user-uploaded files match between their extension and their underlying file type?  As far as I know, that's the only option we have along these lines. 

From the form design side, all you can do is validate (require or restrict) certain extensions, as in just the superficial file extension.

HI Mike,

we are allowing user to upload PDF fils but insdie pdf file it may contains PNG or JPG or invalid content so when we sending the documents to external system though the integration which have received from the user.

while sending the document to external system via integration ,we are checking the below connector function to eliminate the multipart content value.

a!httpFormPart(
name: "multiparts",
contentType: "auto-detect",
value: todocument(documentId)
)

as per external system will  allow the if document is pdf then content type should be application/pdf  but above function we gives the Content-Type: application/x-tika-ooxml while sending to extenal system due to that reason those documents are not moving to  external system due to multipart content.

to eliminate the those issues we thought to check the while user uploading files via upload file at initial time.is there any possibility to verify before uploading files?

Thanks In advance

I'm unclear if you confirmed whether or not you've tried this setting.  Beyond this, it might be beyond the scope of Appian to check, beyond using extra functionality like a plug-in (as stefan mentions below).

I'm unclear if you confirmed whether or not you've tried this setting.  Beyond this, it might be beyond the scope of Appian to check, beyond using extra functionality like a plug-in (as stefan mentions below).

if we enable this option in admin console whether this restriction will apply when we will get the documents from external system via WEB API at case creation time? if it apply  then how we can give response to user to get notify? the document is not valid type