@test29998411 the first approach might work as long as the fields or column names are fixed.
The second approach of using labels is better suited if your tables have fixed number of rows and follow a pattern.
The third approach of splitting the file can be used for large files. Splitting a file based on tables or labels might not improve the extraction.
Training is done with a minimum of 5 documents with the form having all the required fields or values you expect to extract. If you want to add more document formats you can always train a new model and create a composite model using all your models to extract different document formats.
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