Q. Turnitin has returned an error with your submission: “Your submission must contain 20 words or more.”
In this case it's likely that your paper is either scanned or has insufficient selectable text or, if it’s in PDF format, it is an image file instead of text.
To resolve this issue, you can simply add 20 words of text to your document. However, please note this will not generate an appropriate similarity report as the document would still be largely image based. This is only suitable for submissions where a similarity report is not required (such a placement portfolio).
Where a similarity report is expected the document need to be submitted with selectable text.
To check if the PDF is an image or text:
Open the document in your PDF reader. Attempt to select some text - if the range of characters you choose are highlighted as expected, then it's text! If not, it is an image-based PDF.
So, in this case try opening your original document (if it is a word document and re-saving as PDF) or if it is a scanned document then add some text.
The links below has very useful information: