pdfrw

Install the library using `pip` or `conda` for the correct Python environment:
```python
pip install pdfrw
# or if using Anaconda
conda install pdfrw
```

Import the `PdfReader` class explicitly and use it to instantiate the reader object:
```python
from pdfrw import PdfReader

pdf_file = PdfReader('your_document.pdf')
```

This is a known limitation for `pdfrw` regarding full Unicode support in all contexts. For text strings, try to ensure they are ASCII compatible if possible for direct manipulation. If dealing with annotations containing Unicode characters, it often requires embedding a subset CID font, which `pdfrw` may not fully support. Developers sometimes resort to converting non-ASCII text to images or using other PDF libraries that offer better Unicode handling for specific use cases.

No direct code fix exists within `pdfrw` itself for invalid PDFs. A common approach is to pre-process or 'repair' the PDF using another robust PDF tool before `pdfrw` attempts to read it. This can involve using command-line utilities like `pdftk` or Python libraries like `PyMuPDF` to clean the PDF structure. For example, using `PyMuPDF` to create a 'cleaned' version:
```python
import sys
from io import BytesIO
from pdfrw import PdfReader
import pymupdf

def tolerant_reader(fname, password=None):
    idata = open(fname, "rb").read()
    ibuffer = BytesIO(idata)
    try:
        return PdfReader(ibuffer) # Try pdfrw first
    except Exception: # pdfrw failed, attempt repair with PyMuPDF
        doc = pymupdf.open("pdf", ibuffer)
        if password is not None:
            rc = doc.authenticate(password)
            if not rc > 0:
                raise ValueError("wrong password")
        c = doc.tobytes(garbage=3, deflate=True) # Clean and deflate
        del doc
        return PdfReader(BytesIO(c)) # Let pdfrw retry with cleaned data

# Usage example:
pdf = tolerant_reader("your_corrupt.pdf")
```

Implement checks to ensure the PDF object or its attribute exists and is not `None` before attempting to access it. If dealing with potentially encrypted PDFs, ensure `pdfrw`'s `decrypt=True` option is used, and gracefully handle cases where encryption information might be absent or malformed.
```python
from pdfrw import PdfReader

try:
    reader = PdfReader('your_document.pdf', decrypt=True) # Try with decrypt
    if reader.Info is not None and hasattr(reader.Info, 'Length'):
        # Safely access reader.Info.Length
        print(f"Document Length: {reader.Info.Length}")
    else:
        print("PDF Info dictionary or 'Length' attribute not found or is None.")
except Exception as e:
    print(f"An error occurred while reading the PDF: {e}")
```