How to encode/decode correctly using NetSuite file upload in Suitelet

I was able to get a .rtf to upload with the correct contents (simple text phrase: "This is text") using the following:

// Getting File from NS File Field
                var fileObj = context.request.files['custpage_file'];
                // Setting Folder in File Cabinet
                fileObj.folder = 214960;
                var fileId = fileObj.save();
                // Getting/Logging File Contents
                var fileContents = fileId.getContents();
                log.debug({title: 'File Contents', details: fileContents});
                // File Contents = UEsDBBQABgAIAAAAIQDfpNJsWgEAACAFAAATAAgCW0NvbnRlbnRfVHlwZXNdLnhtbCCiBAIooAACAAAAAAAAAAAAAAAAA

                // Decode the String
                var decodedStr = fromBase64(fileContents);
                log.debug({title: 'Decoded Contents', details: decodedStr});

                var headerObj = {};

                // Upload Request
                var res = https.request({
                    method: https.Method.POST,
                    url: 'https://content.dropboxapi.com/2/files/upload',
                    body: decodedStr,
                    headers: headerObj
                });

function fromBase64(stringInput){
            return encode.convert({
                string: stringInput,
                inputEncoding: encode.Encoding.BASE_64,
                outputEncoding: encode.Encoding.UTF_8
            });
        }

However, .docx and .pdf are not uploading with any content. Are those supposed to be in UTF_8 as well? Are there differences between the types of files. I'm just looking to upload .ai and .pdf file formats.