Turnitin will generate a similarity report for files in the following formats:

Microsoft Word
PowerPoint
PDF
HTML
RTF
OpenOffice (ODT)
WordPerfect
PostScript
Hangul (HWP)
Google Docs, Google Slides, Google Sheets (submitted via the Google Drive submission option)
Plain text files

Turnitin's file requirements for submissions provides more information.

Please keep in mind that Canvas does not support all of the file types that will generate a Turnitin Similarity Report and Turnitin will not generate a report for Apple Pages. Compatible text files that can be uploaded to Canvas include the following:

PDF - Portable Document Format
DOC, DOCX - Microsoft Word document
PPT, PPTX - PowerPoint document
XLS, XLSX - Excel document
Pages - Apple iWork Pages document
TXT - Plain text files
RTF - Rich Text Format
ODT, ODF - Open Document
HTML - HyperText Markup Language
Google Docs, Google Slides, Google Sheets (submitted via the Google Drive submission option)