Merging Docx files into one - Apex

Question

I have a requirement, which I should merge two or more word files (.docx) together into one file.

because I can't do arithmetic operations on Blob - I converted it to hex, made the arithmetic, converted it to blob again, and then I tried to save it inside the versionData.

But it saves only the first doc and not both.

I tried to do the following : (the hardcoded Ids is just for testing)

 List<ContentVersion> cdlList =  [SELECT Id,Title,ContentDocumentId,FileType,VersionData FROM ContentVersion WHERE ContentDocumentId='0691l000001DoBTAA0' OR ContentDocumentId='0691l000001DoE3AAK'];
 List<ContentVersion> cvList = new List<ContentVersion>();    
 String combinedDataAsHex = EncodingUtil.convertToHex(cdlList[0].VersionData) + EncodingUtil.convertToHex(cdlList[1].VersionData);
 ContentVersion testContentInsert = new ContentVersion();
 testContentInsert.Title = 'Test';
 testContentInsert.VersionData = EncodingUtil.convertFromHex(combinedDataAsHex);
 testContentInsert.PathOnClient = '/' + cdlList[0].title + '.docx' ;
 cvList.add(testContentInsert);

    
    
 insert cvList;

Is there something I missed? Another way to do it?

Thanks.

Answer 1

Aside from plain text files (e.g. source code or README.TXT type files), most files follow an internal structure. This means that two similar files (e.g. two GIF or DOCX) being "added together" would result in an invalid file structure. Let me give you an example using plain text; we'll choose XML.

File A

<?xml version="1.0" encoding="UTF-8"?>
<request>
  <param1>Hello World</param1>
</request>

File B

<?xml version="1.0" encoding="UTF-8"?>
<request>
  <param2>Goodbye World</param2>
</request>

If you were to combine these two files together as you demonstrated in your question, the result would be:

<?xml version="1.0" encoding="UTF-8"?>
<request>
  <param1>Hello World</param1>
</request>
<?xml version="1.0" encoding="UTF-8"?>
<request>
  <param2>Goodbye World</param2>
</request>

But this isn't valid XML. There must be only one preprocessor command, and one root element. The correct file would be:

<?xml version="1.0" encoding="UTF-8"?>
<request>
  <param1>Hello World</param1>
  <param2>Goodbye World</param2>
</request>

You can't get this by just adding one file to the other, you need to understand the internal structure and adapt.

Similarly, to get two DOCX to work as one, you'd have to decompress both (they're ZIP files), unpack the XML files, recombine, recompress (back to a single ZIP), and then output that result.

This is technically possible in Apex, but you're much better off shipping the files offsite to a Heroku app or something, where you'll have much better CPU performance and fewer restraints, plus actual binary support that Apex is notorious for lacking.