How to Merge PDF Files in Business Central Using a Python API

 

When working with documents in Microsoft Dynamics 365 Business Central, sometimes we need to combine multiple PDF files into a single document — for example, when generating a bundle of invoices or reports.

In this post, I’ll show you how to achieve that by integrating Business Central AL code with a Python-based API using FastAPI and PyPDF2.

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🐍 The Python API (FastAPI + PyPDF2)

We’ll expose a /merge-pdf endpoint using FastAPI that:

• Accepts a list of PDFs encoded in Base64

• Merges them using PyPDF2.PdfMerger

• Returns the combined PDF as a Base64 string

Here’s the Python code:

python

from fastapi import FastAPI, Header, HTTPException
from pydantic import BaseModel
import base64
from PyPDF2 import PdfMerger
from io import BytesIO

app = FastAPI()

class PDFRequest(BaseModel):
    archivos_pdf: list[str]  # List of Base64 PDF files

class PDFResponse(BaseModel):
    pdf_unido: str  # Base64-encoded merged PDF

API_KEY = "YourApiKey"

@app.post("/merge-pdf", response_model=PDFResponse)
async def unir_pdf(data: PDFRequest, x_api_key: str = Header(None)):
    if x_api_key != API_KEY:
        raise HTTPException(status_code=401, detail="Unauthorized access")

    merger = PdfMerger()
    for archivo_base64 in data.archivos_pdf:
        archivo_pdf = BytesIO(base64.b64decode(archivo_base64))
        merger.append(archivo_pdf)

    pdf_unido_io = BytesIO()
    merger.write(pdf_unido_io)
    merger.close()
    pdf_unido_io.seek(0)
    
    return PDFResponse(pdf_unido=base64.b64encode(pdf_unido_io.read()).decode('utf-8'))

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⚙️ The AL Code in Business Central

Here’s the AL codeunit that sends the list of PDF Base64 strings to the Python API:

al

codeunit 50149 MergePDF
{
    procedure MergePdfAPI(PDFsBase64: List of [Text]) PDFUnidoBase64: Text
    var
        Client: HttpClient;
        RequestMsg: HttpRequestMessage;
        ResponseMsg: HttpResponseMessage;
        Content: HttpContent;
        JsonRequest: JsonObject;
        JsonArrayPDFs: JsonArray;
        JsonResponse: JsonObject;
        JsonToken: JsonToken;
        ResponseText: Text;
        Url: Text;
        I: Integer;
        JsonText: Text;
        Headers: HttpHeaders;
        RequestHeaders: HttpHeaders;
    begin
        Url := 'http://"YourIPAddress":YourPort/merge-pdf';
        Clear(JsonRequest);
        Clear(JsonArrayPDFs);

        for I := 1 to PDFsBase64.Count() do
            JsonArrayPDFs.Add(PDFsBase64.Get(I));
        JsonRequest.Add('archivos_pdf', JsonArrayPDFs);
        JsonRequest.WriteTo(JsonText);

        Content.WriteFrom(JsonText);
        Content.GetHeaders(Headers);
        Headers.Clear();
        Headers.Add('Content-Type', 'application/json');

        RequestMsg.Method('POST');
        RequestMsg.SetRequestUri(Url);
        RequestMsg.Content(Content);

        RequestMsg.GetHeaders(RequestHeaders);
        RequestHeaders.Add('x-api-key', 'YourApiKey'); // API Key

        if Client.Send(RequestMsg, ResponseMsg) then begin
            ResponseMsg.Content().ReadAs(ResponseText);

            if ResponseMsg.IsSuccessStatusCode() then begin
                JsonResponse.ReadFrom(ResponseText);
                if JsonResponse.Get('pdf_unido', JsonToken) then
                    PDFUnidoBase64 := JsonToken.AsValue().AsText()
                else
                    Error('No merged PDF received.');
            end else
                Error('API Error: %1', ResponseText);
        end else
            Error('Connection to API failed.');
    end;
}

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✅ Benefits of This Integration

• No need for third-party components inside Business Central

• Flexible — works with any external Python service

• Easy to deploy and extend