Hi,

I think it would be more formal and more idiomatic to say 'please find attached'.

It's best to avoid apostrophes, so you could phrase it as: 'Please find attached the documents signed by .....' or 'please find enclosed'

You should write:
I am attaching documents signed by (...)

Spanish term (edited): documents firmados de la sociedad

The question does not identify the individual who signed the documents, so you can't write '... signed by ...', which requires the name of the person who held the pen when the document was signed.

Adjunto los documentos firmados por (nombre de sociedad)
-->
I am attaching the signed documents from (company name).

or:

I am attaching the documents signed on behalf of (company name).

Spanish term (edited): Adjunto los documentos firmados por la sociedad X

In actual US & UK legal practic/se rather than in a grammatically and syntactically perfect world, a sloppy and albeit colloquial turn of phrase like the 'company's signed docs.' is feasible in foreshortening: 'executed by the authorised signatories' (company's officers), as AT remarks.

Any objection to that turn of phrase would - by company law practitioners - be considered trivial, petty and out of touch with reality.

I doubt any UK or US etc. Companies Registrar or Companies Court Officer has turned down any corporate-related application because of use of this shorthand.