You can't make up function calls and expect them to work. Where in the (already linked) Microsoft Documentation did you find that the ->ConvertToText method exists on the Cell object?

Following the approach I outlined above with the interactive testing window of Microsoft Word, I used the following snippet to get at the text content of an arbitrary cell:

set T = activeDocument.Tables.Item(1)
print T.Cell(2,2).Range.Text
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Translating this to Perl would be something like this:

print $table->Cell(2,2)->Range->Text
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