this.markpdf.convertFile(file, { mode: "fast" }).subscribe({
  next: (markdown) => this.markdown.set(markdown as string),
  error: (err: HttpErrorResponse) => {
    console.error(err.status, err.error); // err.error es el body { error: string } de tu backend
  },
});

import { markpdfErrorInterceptor, MarkpdfClientError } from "@markpdf/angular";
import { provideHttpClient, withInterceptors } from "@angular/common/http";

provideHttpClient(withInterceptors([markpdfErrorInterceptor]));

this.markpdf.convertFile(file, { mode: "fast" }).subscribe({
  next: (markdown) => this.markdown.set(markdown as string),
  error: (err: MarkpdfClientError) => {
    switch (err.kind) {
      case "rate-limit":
        this.showToast("Too many requests, retry in a few seconds.");
        break;
      case "payload-too-large":
        this.showToast("The file is too large.");
        break;
      case "vavalidation":
        this.showToast("Invalid file.");
        break;
      default:
        this.showToast("Could not convert the document.");
    }
  },
});

class MarkpdfClientError extends Error {
  kind: "bad-request" | "forbidden" | "payload-too-large" | "unsupported-media" |
        "vavalidation" | "rate-limit" | "server-error" | "network";
  statusCode: number | null;
  detail: string;
}

import { retry, timer } from "rxjs";

this.markpdf.convertFile(file, { mode: "fast" }).pipe(
  retry({
    count: 3,
    delay: (error, retryCount) => {
      if (error.status !== 429) throw error; // only retries 429
      return timer(2 ** retryCount * 1000);
    },
  })
).subscribe(/* ... */);