Feature Request: Allow selectable attachements to PDF

[0xD0M1M0]

Summary

Enhance PDF on Submit so invoice PDFs can include multiple user-selected attachment files, remain compatible with the e-invoicing standard, let users see the full invoice in Draft (Print Preview / same content as final PDF where the print format allows), and show selected attachments in the printed/PDF output (e.g. annex list).

Context

Today, PDFs are generated on submit; Sales Invoice can embed XML via optional eu_einvoice.

Requirements

1. Attachments: Users can pick several existing files to ship with the invoice PDF as attachements to the PDF. If installed, the e-invoice XML with the same attachements) should be attached as well.
2. E-invoicing: Output must match the agreed standard (EN 16931 / XRechnung / ZUGFeRD, etc.); norm validation likely lives in eu_einvoice, not only in pdf_on_submit.
3. Draft preview: View the complete invoice before submit (reuse standard Print/Preview with the same print format, and/or a “Preview like after submit” action).
4. Print: Print format should list chosen attachments (and embed them in PDF only if merge/embedding is in scope).

Supporting documentation

OZG-RE: Size limits
Content integrity
X-Rechnung: Chapter 8.2 Binary Object and 11.2 Additional Supporting Documents

(LMK-16)

[dafrose]

@barredterra, @0xD0M1M0: I have a question regarding the integration into the print format: A possible solution would be to introduce a child table into Sales Invoice where you can list attached files. You get an ordered list that can be referenced via doc in the print format and thus be included in the "main" printed invoice document. This could also be the technical basis for merging/annexing/embedding additional attachments into the combined output file.

Does it make sense to introduce such a child table via pdf-on-submit or rather via erpnext core?

[barredterra]

Does it make sense to introduce such a child table

Attachments in child tables have rather bad UX, so I'd only use it for data-storage combined with custom UI.

pdf-on-submit or rather via erpnext core

I don't think ERPNext would accept this.

[dafrose]

Summary after talking to both of you: Child Table is a valid implementation option for getting an ordered list of attachments. However, adding attachments directly via an attachment field in the child table is rather irritating in terms of how well it works with Frappe's UI. An additional (nice-to-have) option would be to either add an "attachment drop area" where you can drag and drop attachments into or (possibly simpler) a button that triggers the attach file dialog with some additional text input to populate the child table with an output name.

[dafrose]

Regarding data types @barredterra and @0xD0M1M0: Should file types other than PDF be converted to PDF automatically on merge or be blocked? For images, conversion should be straight-forward. For Word-like documents it might be fine (could break formatting) for Excel-Sheets the probability of a bad result is high.

[0xD0M1M0]

For e-invoice (X-Rechnung) these is a set of allowed documents:
• application/pdf (.pdf)
• image/png (.png)
• image/jpeg (.jpg)
• text/csv (.csv)
• application/vnd.openxmlformats-officedocument.spreadsheetml.sheet (.xslx)
• application/vnd.oasis.opendocument.spreadsheet (.ods)

[dafrose]

That list makes sense, when embedding files into XML, but does it also make sense when merging everything into one PDF? Btw. it is also possible to embed data sheets into PDFs but that's a totally different rabbit hole.

[0xD0M1M0]

not merging into one PDF, but attaching

[dafrose]

Ok, thanks for the clarification. Embedding attachments into PDF is new to me, so I went down the mental path of PDF merging. I'll look into that but it makes sense to follow the same restrictions as e-invoice in that case.

[dafrose]

After some more discussion it is now clear, that this is a Sales-Invoice-specific feature request that can live completely inside eu_einvoice. I will open a new issue on that repo. For pdf_on_submit I am planning to replace the current call to attach_xml_to_pdf with a hook that can be tied into from eu_einvoice. That is more generic and reusable than the current solution and makes more sense for a more elaborate process than "take my pdf and give it back with some XML".