Detect File Format and Check Format Compatibility

Sometimes it is necessary to determine the format of a document before opening because the file extension does not guarantee that the contents of the file are appropriate. For example, it is known that Crystal Reports often outputs documents in RTF format, but gives them the .doc extension.

Aspose.Words provides an ability to obtain information about the file type in order to avoid an exception if you are not sure what the actual content of the file is.

Detect File Format without an Exception

When you are dealing with multiple documents in various file formats, you may need to separate out those files that can be processed by Aspose.Words from those that cannot. You may also want to know why some of the documents cannot be processed.

If you attempt to load a file into a Document object and Aspose.Words cannot recognize the file format or the format is not supported, Aspose.Words will throw an exception. You can catch those exceptions and analyze them, but Aspose.Words also provides the DetectFileFormat method that allows us to quickly determine the file format without loading a document with possible exceptions. This method returns a FileFormatInfo object that contains the detected information about the file type.

DetectFileFormat only checks the file format but does not validate the file format. There is no guarantee that the file will be opened successfully, even if DetectFileFormat returns that it is one of the supported formats. This is because of DetectFileFormat method reads only partial file format data, sufficient for checking the file format, but not enough for complete validation.

Check Files Format Compatibility

We can check the format compatibility of all files in the selected folder and sort them by format into corresponding subfolders.

Since we are dealing with contents in a folder, the first thing we need to do is get a collection of all the files in this folder using the GetFiles method of the Directory class (from the System.IO namespace).

The following code example shows how to get a list of all the files in the folder:

When all the files are collected, the rest of the work is done by the DetectFileFormat method, which checks the file format.

The following code example shows how to iterate over the collected list of files, check the format of each file, and moves each file to the appropriate folder:

The files are moved into appropriate subfolders using the Move method of the File class, from the same System.IO namespace.

The following files are used in the example above. The file name is on the left and its description is on the right:

Group of Files	Input Document	Type
Supported file formats	Test File (DOC).doc	Microsoft Word 95/6.0 or Microsoft Word 97 – 2003 document.
	Test File (DOT).dot	Microsoft Word 95/6.0 or Microsoft Word 97 – 2003 template.
	Test File (DOCX).docx	Office Open XML WordprocessingML document without macros.
	Test File (DOCM).docm	Office Open XML WordprocessingML document with macros.
	Test File (DOTX).dotx	Office Open XML WordprocessingML template.
	Test File (DOTM).dotm	Office Open XML WordprocessingML template with macros.
	Test File (XML).xml	FlatOPC OOXML Document.
	Test File (RTF).rtf	Rich Text Format document.
	Test File (WordML).xml	Microsoft Word 2003 WordprocessingML document.
	Test File (HTML).html	HTML document.
	Test File (MHTML).mhtml	MHTML (Web archive) document.
	Test File (ODT).odt	OpenDocument Text (OpenOffice Writer).
	Test File (OTT).ott	OpenDocument Document Template.
	Test File (DocPreWord60).doc	Microsoft Word 2.0 document.
Encrypted documents	Test File (Enc).doc	Encrypted Microsoft Word 95/6.0 or Microsoft Word 97 – 2003 document.
	Test File (Enc).docx	Encrypted Office Open XML WordprocessingML document.
Unsupported file formats	Test File (JPG).jpg	JPEG image file.

FAQ

Q: How can I determine the file format of a document without loading it into a Document object?
A: Use the static method FileFormatUtil::DetectFileFormat and pass the file path. It returns a FileFormatInfo object that contains properties such as GetFileFormatType() and IsEncrypted. This call reads only the header bytes, so no Document is created and no exception is thrown for unsupported formats.
Q: What information does FileFormatInfo provide for encrypted files?
A: The IsEncrypted property of FileFormatInfo is set to true when the detected format is encrypted. You can still obtain the file format type, but you must provide the correct password when later loading the file with Document.
Q: How can I check whether a detected format is supported by the current Aspose.Words version before attempting to load it?
A: Compare the FileFormatInfo::GetFileFormatType() value against the FileFormat enumeration. All values listed in the enumeration are supported. If the value is FileFormat::Unknown or FileFormat::Unsupported, skip loading or handle the file separately.
Q: Why does DetectFileFormat sometimes report a supported format, yet loading the document still throws an exception?
A: DetectFileFormat reads only a small portion of the file to identify the format. Corrupted files, partially downloaded files, or files that contain unsupported features may still be identified as a known format but fail during full parsing. In such cases, catch the exception from Document construction and log the detailed error message.
Q: Can DetectFileFormat differentiate between DOC and DOCX files that share the same .doc extension?
A: Yes. The method examines the file header, so a DOCX (Office Open XML) file will be reported as FileFormat::Docx even if its extension is .doc. This allows you to correctly handle files regardless of their extensions.

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