The maximum file size that can be submitted to Turnitin is 40mb.
Turnitin can process the following valid file types: Microsoft Word (.doc), Portable Document Format (.pdf), Postscript (.ps), Text (.txt), HTML (.htm, .html), WordPerfect (.wps) and Rich Text Format (.rtf).
Microsoft Excel and PowerPoint documents cannot be accepted.
Following student submission of assignment files to Moodle, there is no defined time within which the Turnitin service will return similarity scores and originality report.
However, you should allow up to 48 hours before contacting the e-Learning team to report any issues.
"No, work submitted within a single assignment by a particular student will never match other submissions within the same assignment by themselves." 
"No, an unoriginality score of 0% does not guarantee the work is not plagiarised. Turnitin has a large database of web sites, books, journal papers and other sources, but does not (and cannot) include everything ever written." 
 UCL Learning Technology Support Service. How to view and interpret the Turnitin similarly score and originality reports. University College London. Available from: http://go.bath.ac.uk/ylub [Accessed 20 June 2011]